7th International Fermi Symposium

Congress Center Garmisch-Partenkirchen

Congress Center Garmisch-Partenkirchen

Richard-Strauss-Platz 1A, 82467 Garmisch-Partenkirchen Germany
Jochen Greiner (MPE Garching), Julie McEnery (GSFC/NASA)



This symposium follows previous Fermi Symposia at


The two Fermi instruments have been surveying the high-energy sky since August 2008. The Large Area Telescope (LAT) has discovered more than three thousand gamma-ray sources and many new source classes, bringing the importance of gamma-ray astrophysics to an ever-broadening community. The LAT catalog includes supernova remnants, pulsar wind nebulae, pulsars, binary systems, novae, several classes of active galaxies, starburst galaxies, normal galaxies, and a large number of unidentified sources. Continuous monitoring of the high-energy gamma-ray sky has uncovered numerous outbursts from a wide range of transients. Fermi LAT's study of diffuse gamma-ray emission in our Galaxy revealed giant bubbles, as well as an excess of gamma-rays from the Galactic center region, both observations have become exciting puzzles for the astrophysics community.  The direct measurement of a harder-than-expected cosmic-ray electron spectrum may imply the presence of nearby cosmic-ray accelerators. LAT data have provided stringent constraints on new phenomena such as supersymmetric dark-matter annihilations as well as tests of fundamental physics. The full reprocessing of the entire mission dataset with Pass 8 includes improved event reconstruction, a wider energy range, better energy measurements, and significantly increased effective area, all them boosting the discovery potential and the ability to do precision observations with LAT. The Gamma-ray Burst Monitor (GBM) continues to be a prolific detector of gamma-ray transients: magnetars, solar flares, terrestrial gamma-ray flashes and gamma-ray bursts at keV to MeV energies, complementing the higher energy LAT observations of those sources in addition to providing valuable science return in their own right.

All gamma-ray data are made immediately available at the Fermi Science Support Center (http://fermi.gsfc.nasa.gov/ssc). These publicly available data and Fermi analysis tools have enabled a large number of important studies. We especially encourage guest investigators worldwide to participate in this symposium to share results and to learn about upcoming opportunities.

This meeting will focus on the new scientific investigations and results enabled by Fermi, the mission and instrument characteristics, future opportunities, coordinated observations and analysis techniques. In particular, we also encourage discussion of future prospects/science with Fermi in preparation for the upcoming NASA senior review.

    • 5:00 PM 6:00 PM
      Start of Registration 1h
    • 6:00 PM 8:00 PM
      Welcome Reception
      Convener: LOC
    • 9:00 AM 10:10 AM
      Opening Session


      Convener: Elizabeth Hays (NASA GSFC)
      • 9:00 AM
        Opening 10m
        Speaker: Elizabeth Hays (NASA GSFC)
      • 9:10 AM
        Welcome by NASA HQ 10m
        Speaker: Stefan Immler (NASA Headquarters)
      • 9:20 AM
        Remembering Neil Gehrels 20m
        Speaker: John Nousek (Penn State University)
      • 9:40 AM
        Status of Fermi 30m
        Speaker: Elizabeth Hays (NASA GSFC)
    • 10:10 AM 10:40 AM
      Break 30m
    • 10:40 AM 12:10 PM
      Pulsars I
      Convener: Robin Corbet
      • 10:40 AM
        Pulsars: implications from Fermi LAT observations and future prospects 30m

        Gamma-ray observations with the Fermi Large Area Telescope (LAT) have revealed significant pulsations from more than 200 young and recycled, millisecond pulsars. These observations have demonstrated that pulsars are by far the largest source class in the Galactic plane at GeV energies, and more gamma-ray pulsars are still being revealed by the LAT. In this talk I will give an overview of the main results from Fermi LAT pulsar observations, and from studies of unassociated LAT sources likely to contain pulsars. I will discuss some of the implications of these results in terms of population statistics and high-energy pulsar emission properties.

        Speaker: Lucas Guillemot (LPC2E and Universite d'Orleans)
      • 11:10 AM
        Order parameters for the high-energy spectra of pulsars 15m

        From the hundreds of gamma-ray pulsars known, only a handful show non-thermal X-ray pulsations. Instead, nine objects pulse in non-thermal X-rays but lack a counterpart at higher energies. What order parameters describe the spectral variety, making the pulsars GeV and/or X-ray bright? Can observations in only one portion of the spectra predict detectability in the other? Can we expect a population of MeV-peaking pulsars? We normally fit observational spectra just with phenomenological functions (a power law with a cutoff in gamma-rays, or a log parabola from X-rays up). Here we shall present the results of a relatively simple physical model for the magnetospheric emission of pulsars above 1 keV, with which we start tacking these questions. It is based on synchro-curvature emission, and includes 1D time-dependent particle propagation. The model seems to contain the basic ingredients needed to describe all observed spectra well: With just four physical parameters, we can fit gamma/X-ray pulsar spectra along seven orders of magnitude, providing an interpretation for the appearance of sub-exponential cutoffs at high energies, or the flattening of the X-ray spectra at soft energies.

        Speaker: Diego Torres (ICREA & Institute of Space Sciences)
      • 11:25 AM
        The first detection of a pulsar with the Atacama Large Millimetre Array 15m

        We used the Atacama Large Millimetre Array (ALMA) to observe the Vela pulsar (PSR B0833-45), one of the very few pulsars observed in radio and from the mid-infrared up to the very high-energy gamma-rays. We detected Vela at frequencies of 97.5, 145, 233, 343.5 GHz and found that its energy density spectrum follows a power-law. The ALMA fluxes correspond to high brightness temperatures suggesting that this emission is due to a coherent radiative process. This is, therefore, the first indication of coherent emission reaching the submillimetre regime in pulsars. Moreover, we identified an extended structure, preliminarily detected in ground-based observations. We support its interpretation as a counter-jet protruding from the pulsar.

        Speaker: Bronislaw Rudak (Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences)
      • 11:40 AM
        Understanding the Pulsar High Energy Emission: Macroscopic and Kinetic Models vs. Fermi Data 15m

        I will show that Fermi data provide crucial information that guides us to yield meaningful constraints on the macroscopic parameters of our global dissipative pulsar magnetosphere models. Our FIDO (Force-Free Inside, Dissipative Outside) models indicate that the dissipative regions lie outside the light cylinder near the equatorial current sheet. Our models reproduce the light-curve phenomenology while a detailed comparison of the model spectral properties with those observed by Fermi reveals the dependence of the macroscopic conductivity parameter on the spin-down power. We further exploit these important results by building self-consistent 3D global kinetic particle-in-cell (PIC) models, which, eventually, provide the dependence of the macroscopic parameter behavior (e.g. conductivity) on the microphysical properties (e.g. particle multiplicities). Our PIC models provide field structures and particle distributions that are not only consistent with each other but also able to reproduce a broad range of the observed gamma-ray phenomenology (light curves and spectral properties) of both young and millisecond pulsars. The convergent results of our macroscopic and kinetic models and their agreement with the Fermi data provide a unique insight into the understanding of the physical mechanisms behind the high-energy emission in pulsar magnetospheres.

        Speaker: Constantinos Kalapotharakos (NASA GSFC, UMCP)
      • 11:55 AM
        MeV Pulsars: Modeling Spectra and Polarization 15m

        A sub-population of energetic rotation-powered pulsars show high fluxes of pulsed non-thermal hard X-ray emission. While this ‘MeV pulsar’ population includes some radio-loud pulsars like the Crab and PSR B1509-58, a significant number have no detected radio or GeV emission, a mystery since gamma-ray emission is a common characteristic of pulsars with high spin-down power. The All-Sky Medium-Energy Gamma-Ray Observatory (AMEGO), as well as e-Astrogam, plan to detect emission and polarization in the MeV band and may shed light on the MeV pulsars. We present a model for the spectrum and polarization of MeV pulsars where the X-ray emission comes from electron-positron pairs radiating in the outer magnetosphere and current sheet. This model predicts that the peak of the SED increases with surface magnetic field strength if the pairs are produced in polar cap cascades. For small inclination angles, viewing at large angles to the rotation axis can miss both the radio pulse and the GeV pulse from particles accelerating near the current sheet. Characterizing the emission and geometry of MeV pulsars can thus provide clues to the source of pairs and acceleration in the magnetosphere.

        Speaker: Alice Harding (NASA Goddard)
    • 12:10 PM 1:30 PM
      Catered Lunch 1h 20m
    • 1:30 PM 3:30 PM
      Active Galactic Nuclei: I GaPa/2-1 - Konzertsaal (Garmisch-Partenkirchen)

      GaPa/2-1 - Konzertsaal


      Convener: Elisabetta Cavazzuti (Italian Space Agency)
      • 1:30 PM
        The Gamma-Ray Lobes of Centaurus A 15m

        The broadband emission from the lobes of radio galaxy Centaurus A (Cen A) has been widely considered to be produced via a simple leptonic model, i.e., synchrotron and inverse-Compton scattering. More recently, gamma-ray data from the Fermi Large Area Telescope (LAT) has hinted at a spatial mismatch with the radio and microwave images of the Cen A lobes, challenging the simple leptonic scenario. We present a morphological analysis of the Cen A lobes, confirming this phenomenon and providing a full 9 year Pass 8 LAT gamma-ray image of the lobes. In light of this analysis, we offer alternative production scenarios which may account for the observed mismatch.

        Speaker: Jeff Magill (UMD / GSFC)
      • 1:45 PM
        VLBI and gamma-ray studies of TANAMI radio galaxies 15m

        The $\gamma$-ray sky is strongly dominated by blazars, i.e. AGN with relativistic jets oriented closely with our line of sight. Radio galaxies are their misaligned counterparts, and make up about ∼ 1-2% of all AGN observed by Fermi-LAT. Nonetheless, they provide us with a view of AGN jets which is less biased by Doppler boosting effects, and allow us to test jet production and emission models in light of the unified scheme of radio-loud AGN. The combination of $\gamma$-ray data and high-resolution Very Long Baseline Interferometry (VLBI) studies is a powerful tool in order to investigate these objects. We present selected results of an ongoing study focused on the radio galaxies in the southern-hemisphere VLBI (and multi-wavelength) monitoring program TANAMI.

        Speaker: Roberto Angioni (Max Planck Institute for Radioastronomy)
      • 2:00 PM
        RoboPol: the optical polarisation of gamma-ray-loud and gamma-ray-quiet blazars 15m

        The RoboPol program has been monitoring an unbiased sample of blazars since 2013 with a cadence of less than a few days. The main drive has been to quantify their optical polarisation properties, understand its variability and gain insight in the mechanisms producing the smooth and long rotations of the polarisation angle, in a systematic and unbiased way. Here we focus on the magnitude of polarisation. We present average R-band optopolarimetric data, as well as variability parameters, from the first and second RoboPol observing season. We show that gamma-ray-loud blazars are systematically more polarised than gamma-ray-quiet ones. We however do not find any evidence that this discrepancy is related to the redshift distribution, rest-frame R-band luminosity density, or the source classification. Furthermore, we find that median polarisation fraction drops with the synchrotron-peak-frequency and so is the randomness of the polarisation angle distribution. We propose a scenario which mediates efficient particle acceleration in shocks and increases the helical B-field component immediately downstream of the shock.

        Speaker: Emmanouil Angelakis
      • 2:15 PM
        High-resolution polarization imaging of the Fermi blazars 15m

        Ever since the revolutionary discovery by the Fermi mission that active galactic nuclei (AGN)produce copious amounts of high-energy emission, its origin has remained elusive. Using high-frequency radio interferometry (VLBI) polarization imaging, we could probe the magnetic field topology of the compact high-energy emission regions in blazars. A case study for blazar 3C 279 reveals presence of multiple gamma-ray emission regions. The observed anti-correlation between gamma-ray flux and percentage polarization at optical bands challenges the current high-energy emission models. High-energy polarization observations will be crucial in better understanding the high-energy dissipation mechanisms. I will briefly describe the polarization capabilities of the AMEGO (All-sky Medium Energy Gamma-ray Observatory) mission.

        Speaker: Bindu Rani (NASA GSFC)
      • 2:30 PM
        SALT ToO spectropolarimetry observations of blazars and self-consistent SED and spectropolarimetry modeling of blazars 15m

        We report on recent results from a target-of-opportunity programme to
        obtain spectropolarimetry observations of flaring gamma-ray blazars with
        the Southern African Large Telescope (SALT). In tandem with this observational
        program, we develop a leptonic blazar model for a self-consistent representation
        of SEDs and optical (SALT) spectropolarimetry. Such modeling provides an accurate
        estimate of the degree of order of the magnetic field in the emission region as
        well as thermal contributions (from the host galaxy and the accretion disk) to
        the SED, thus putting strong constraints on the physical parameters of the
        gamma-ray emitting regions.

        Speaker: Markus Boettcher (North-West University)
      • 2:45 PM
        Gamma-rays in the radio galaxy 3C 84: A complex situation 15m

        3C 84 is unique in that it is one of the few non-blazar AGN that is detected at ultra high energies (including MAGIC in addition to Fermi/LAT). The source itself has been increasing in flux density at both radio and Gamma-rays since approximately 2005 with VLBI observations showing that this rising emission is associated with a slowly moving component south of the jet-launching (C1) region, commonly known as "C3". Recent analysis of multi-wavelength Korean VLBI Network data has suggested multiple locations of Gamma-rays within 3C 84. In addition to the slowly rising trend in C3, smaller scale rapid variation of radio and Gamma-ray fluxes are associated with the C1 region, but that the correlations observed are due to random processes. We than applied wavelet analysis using the WISE package to the kinematics of 3C 84 from 2010 until now. We find that a large flare beginning in early 2015 and currently decaying is apparently due to the emission of a new component from the C3 region. Additionally, there appears to be evidence for helical trajectories with Gamma-ray flaring being possibly associated with when the helical path passes through our line-of-sight.

        Speaker: Bindu Rani (NASA GSFC)
      • 3:00 PM
        Magnetospheric Gamma-Ray Emission in AGN 15m

        Radio Galaxies have emerged as unique gamma-ray emitting source class
        on the extragalactic sky. With their jets believed to misaligned such
        that Doppler boosting effects become moderate, they allow for new
        insights into the nuclear source region. I will report on new results
        for M87 and discuss implications of recent findings for Centaurus A. The
        relevance of a magnetospheric gamma-ray contribution in radio galaxies
        will be highlighted and general constraints will be derived to assess
        its plausibility for a given source.

        Speaker: Frank Rieger
      • 3:15 PM
        Constraints on proton synchrotron origin of VHE gamma-rays from the extended jet of AP Librae 15m

        The multi-wavelength photon spectrum from the BL Lac object AP Librae extends from radio to TeV gamma rays. The X-ray to very high energy gamma ray emission from the extended jet of this source has been modeled earlier with inverse Compton (IC) scattering of relativistic electrons off the CMB photons. The IC/CMB model requires the kpc scale extended jet to be highly collimated with bulk Lorentz factor close to 10. Here we discuss the possibility of proton synchrotron origin of X-rays and gamma-rays from the extended jet with bulk Lorentz factor 3. This scenario requires extreme energy of protons 3.98 × 1021 eV and high magnetic field 1 mG of the extended jet with jet power ∼ 5 × 1048 ergs/sec in particles and magnetic field (which is more than 100 times the Eddington’s luminosity of AP Librae) to explain the very high energy gamma ray emission. Moreover, we have shown that X-ray emission from the extended jets of 3C 273 and PKS 0637-752 could be possible by proton synchrotron emission with jet powers comparable to their Eddington’s luminosities.

        Speaker: Dr Nayantara Gupta (Raman Research Institute)
    • 1:30 PM 3:30 PM
      Pulsars: Pulsars II GaPa/1-1 - Olympiasaal (Garmisch-Partenkirchen)

      GaPa/1-1 - Olympiasaal


      Convener: Bronislaw Rudak (Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences)
      • 1:30 PM
        The Search for Millisecond Pulsars 30m

        Millisecond pulsars (MSPs) are old pulsars which have been spun-up to incredible rotation rates by the accretion of matter from an orbiting companion star. Their extreme properties and long-term stability make them valuable objects for a wide variety of fundamental astrophysics. In recent years, the rate of new MSP discoveries has increased dramatically, owing in large part to the "treasure trove" of pulsar-like sources detected within the LAT data. In fact, more than a quarter of all known MSPs were discovered in searches targeting unidentified Fermi-LAT sources. In this talk, I will describe the various contributions that Fermi has made to the MSP search effort, including the latest results from blind searches for gamma-ray pulsations from unknown pulsars. I will also discuss the prospects for future discoveries in these areas, and the implications of Fermi's observations for the Galactic MSP population.

        Speaker: Colin Clark (University of Manchester)
      • 2:00 PM
        On the highest energy emission from millisecond pulsars 15m

        Fermi has detected over 200 pulsars above 100 MeV. In a previous work, using 3 years of LAT data (1FHL catalog) we reported that 28 of these pulsars show emission above 10 GeV; only three of these, however, were millisecond pulsars. The recently-released Third Catalog of Hard Fermi-LAT Sources (3FHL) contains over 1500 sources showing emission above 10 GeV, 17 of which are associated with gamma-ray millisecond pulsars. Using three times as much data as in our previous study (1FHL), we report on a systematic analysis of these 17 pulsars to determine the highest energy (pulsed) emission from millisecond pulsars and discuss the best possible candidates for follow-up observations with ground based TeV instruments (HESS, MAGIC, VERITAS, and the upcoming CTA).

        Speaker: Dr Pablo Saz Parkinson (The University of Hong Kong)
      • 2:15 PM
        Hunting for the missing spiders 15m

        With a growing number of gamma-ray emitting millisecond pulsars (MSPs) discovered by Fermi and by combining multi-wavelength observing facilities, it is now possible to study their properties as a population. One of the successes is the discovery of gamma-ray emitting compact MSP binaries known as black-widow and redback systems and this opens a new window to study pulsars and their evolution. I will discuss how multi-wavelength observations reveal a new population of compact MSP binaries that provides new insight into MSP's emission mechanisms and the physics of compact objects. In particular, I will summarize some recent results of our optical and hard X-ray observing campaigns of gamma-ray emitting black-widows and redbacks, and will also discuss the implications to their evolution.

        Speaker: Albert Kong (National Tsing Hua University)
      • 2:30 PM
        Inductive spikes from the Crab Nebula 15m

        A new theory of the gamma-ray flares from the Crab Nebula is presented, in which the trigger is a sudden drop in the mass-loading of the pulsar wind. The current required to maintain wave activity in the wind is then carried by very few particles of high Lorentz factor. On impacting the Nebula, these particles produce a tightly beamed, high luminosity burst of hard gamma-rays, which reproduces the spectrum, variability timescale and power of the most intense flares. Similar flares potentially contribute to the gamma-ray emission from other powerful pulsars, such as J0537$-$6910 and B0540$-$69.

        Speaker: John Kirk (Max-Planck-Institut fuer Kernphysik)
      • 2:45 PM
        HAWC TeV gamma-ray observations of two extended nebulae surrounding Geminga and PSR B0656+14 constrain the origin of the local positron flux 15m

        Cosmic-ray positrons are charged antiparticles that strike Earth’s atmosphere isotropically. At energies below several GeV they are produced by cosmic-ray protons interacting with nearby interstellar matter. At higher energies, an unexpected and unexplained excess above the proton-induced background has been detected by several satellites, including PAMELA, AMS-02 and Fermi. Due to energy losses in interstellar magnetic and radiation fields, the highest-energy positrons observed must have originated in our immediate Galactic neighborhood. This excess has been theorized to be originated from nearby astrophysical sources, dark matter, or new modes of cosmic-ray secondary production. Amongst the astrophysical sources, pulsars as Geminga and PSR B0656+14 have been proposed to be contributors to this excess. The HAWC Gamma-Ray Observatory reported the discovery of TeV gamma-ray emission extending several degrees around the positions of Geminga and PSR B0656+14 pulsars. Using the morphological and spectral measurements of these two VHE gamma-ray sources, we determine the diffusion coefficient of electrons escaping them and their contribution to the positron flux measured at Earth. For this assumption of isotropic diffusion, we find that neither of these sources make an appreciable contribution to the locally measured positron flux.

        Speaker: Ruben López-Coto (Max Planck Institut für Kernphysik)
      • 3:00 PM
        Observing and modeling the gamma-ray emission from pulsar/pulsar wind nebula complex PSR J0205+6449/3C 58 15m

        We present the results of the analysis of 8 years of Fermi-LAT data of the pulsar/pulsar wind nebula complex PSRJ0205+6449/3C 58. Using a contemporaneous ephemeris, we carried out a detailed analysis of PSRJ0205+6449 both during its off-peak and on-peak phase intervals. 3C 58 is significantly detected during the off-peak phase interval. Hints for a possible flare from 3C 58 are identified. We show that the spectral energy distribution at high energies is the same disregarding the phases considered, and thus that this part of the spectrum is most likely dominated by the nebula radiation. We present results of theoretical models of the nebula and the magnetospheric emission that confirm this

        Speaker: JIAN LI (Institute of Space Sciences (CSIC-IEEC))
      • 3:15 PM
        An Einstein@home blind search for gamma-ray pulsars 15m

        We present the results of the analysis of 13 gamma-ray pulsars discovered in the Einstein@Home blind search survey using Fermi Large Area Telescope (LAT) Pass 8 data. The 13 new gamma-ray pulsars were discovered by searching 118 unassociated LAT sources from the third LAT source catalog (3FGL), selected using the Gaussian Mixture Model (GMM) machine learning algorithm on the basis of their gamma-ray emission properties being suggestive of pulsar magnetospheric emission. The new gamma-ray pulsars have pulse profiles and spectral properties similar to those of previously-detected young gamma-ray pulsars. Follow-up radio observations have revealed faint radio pulsations from two of the newly-discovered pulsars, and enabled us to derive upper limits on the radio emission from the others, demonstrating that they are likely radio-quiet gamma-ray pulsars. We also present results from modeling the gamma-ray pulse profiles and radio profiles, if available, using different geometric emission models of pulsars.

        Speaker: Jason WU (MPIfR)
    • 3:30 PM 4:00 PM
      Coffee Break 30m
    • 4:00 PM 5:00 PM
      NSF/NASA Press Release Streaming
    • 5:00 PM 6:30 PM
      Active Galactic Nuclei: II GaPa/2-1 - Konzertsaal (Garmisch-Partenkirchen)

      GaPa/2-1 - Konzertsaal


      Convener: Elisabetta Cavazzuti (Italian Space Agency)
      • 5:00 PM
        The Third Catalog of Hard Fermi-LAT Sources (3FHL) 15m

        The Third Catalog of Hard Fermi-LAT Sources (3FHL), based on the first 7 years of LAT data using the Pass 8 event-level analysis, contains 1556 sources in the 10 GeV--2 TeV energy range. The sensitivity and angular resolution are improved by factors of 3 and 2 relative to the previous LAT catalog in this energy range (1FHL). Most 3FHL sources (79%) are extragalactic, including 16 sources located at very high redshift (z>2), while 9% are Galactic and 12% are unassociated (or associated with sources of unknown nature). The catalog includes 214 new gamma-ray sources. The substantial increase in the number of photons (more than 4 times the number in 1FHL and 10 times that of 2FHL) also allows us to characterize spectral curvature for 32 sources and flux variability for 163 of them. The 3FHL catalog provides an excellent opportunity to relate observations from space to those accessible from the ground (e.g. H.E.S.S., MAGIC, VERITAS, HAWC, and in the near future the Cherenkov Telescope Array).

        Speaker: David Thompson (NASA Goddard Space Flight Center)
      • 5:15 PM
        Preliminary results from the fourth catalog of AGN Detected by the Fermi-LAT 15m

        Preliminary results of the fourth catalog of active galactic nuclei (AGNs, 4LAC) detected in gamma rays by the Fermi Large Area Telescope (LAT) in seven years of scientific operation are presented. This catalog will be similar to the previously released third LAT AGN catalog (3LAC). The 4LAC includes approximately 2500 gamma-ray sources located at high Galactic latitudes (|b| > 10°) that are detected with a test statistic (TS) greater than 25 and are statistically associated with AGNs. The 4LAC contains many new objects, and most of them are of unknown type and lack spectroscopic information of sufficient quality to determine the strength of their emission lines. Various gamma-ray properties and their correlations are presented and discussed for the different blazar classes. The trends observed in previous catalogs are confirmed. We will present some of the novelties arising in the 4LAC.

        Speaker: Dario Gasparrini (SSDC & INFN PG)
      • 5:30 PM
        MAGIC observations of extreme blazars: Toward clarifying the blazar sequence 15m

        Extreme blazars (EHBLs) are mostly characterized by a synchrotron peak located at energies > 1 keV, and by the hardness of the spectrum in the high-energy (HE, E > 100 MeV) range. So far, only a handful of these objects have been detected at very-high energies (VHE, E > 100 GeV) by Imaging Atmospheric Cherenkov Telescopes. Moreover, multi-wavelength observations of some of these blazars (like 1ES 0229+200) have provided evidence of a VHE gamma-ray emission extending to several TeV, which is difficult to explain naturally with standard, one-zone synchrotron self-Compton models for BL Lac objects. Furthermore, their GeV-TeV spectra also shed new light on the blazar sequence.

        Since 2010, nine EHBLs have been observed in different observing multi-wavelength campaigns of the MAGIC telescopes, aiming to increase the number of known EHBL TeV-emitters. Three sources have been clearly detected at TeV energies by the MAGIC telescopes. In this contribution, I will present the results of the multi-wavelength campaigns. In particular, the GeV-TeV behaviour of these sources will be presented and compared to the known EHBL prototype (1ES 0229+200).

        Speaker: Mr Vandad Fallah Ramazani (University of Turku, Tuorla Observatory)
      • 5:45 PM
        Gamma-ray Blazars at the Dawn of the Universe 15m

        A broadband study of $z>3$ blazars enables us to understand the evolution of the properties of relativistic jets over cosmic time. It has been found in many studies that such high $z$ blazars host $>$billion solar mass black holes and thus shed a new light on the supermassive black hole formation in the early Universe. Here, we report the first gamma-ray detection of blazars beyond $z=3.1$ using the sensitive Pass 8 dataset of Fermi-LAT. These objects are found to host extremely massive black holes at their centers, confirmed both from optical spectroscopy and accretion disk modeling. Further details of the results, including multi-wavelength follow up studies from NuSTAR and XMM-Newton, will be presented within the framework of the disk-jet connection in powerful jetted AGNs. We will also summarize the prospects of hunting these cosmic monsters with the All-Sky Medium Energy Gamma-ray Observatory (AMEGO), a probe concept study for the next NASA decadal survey. In the 200 keV to 10 GeV band, AMEGO will detect these objects by the hundreds and will provide crucial insight about the emission mechanisms powering the relativistic jets of the most powerful blazars in the Universe.

        Speaker: Dr Vaidehi Sharan Paliya (Clemson University)
      • 6:00 PM
        On the radio and GeV-TeV gamma-ray emission connection in Fermi blazars. 15m

        The Fermi-LAT revealed that blazars dominate the census of the gamma-ray sky, and a significant correlation was found between radio and gamma-ray emission in the 0.1-100 GeV energy range. However, the possible connection between radio and very high energy (VHE, E>0.1 TeV) emission still remains elusive, owing to the lack of a homogeneous VHE sky coverage.
        With this work we aim to quantify and assess the significance of a possible connection between the radio emission on parsec scale measured by the very long baseline interferometry and GeV-TeV gamma-ray emission in blazars, which is a central issue for understanding the blazar physics. We use two large and unbiased AGN samples extracted from the 1FHL and 2FHL catalogs, and for comparison, we perform the same analysis by using the 3FGL 0.1-300 GeV gamma-ray energy flux.
        Overall, the radio and gamma-ray emission above 10 GeV turns out to be uncorrelated for all the blazar sub-classes with the exception of high synchrotron peaked objects. Conversely, when 0.1-300 GeV gamma-ray energies are considered, a strong and significant correlation is found for all of the blazar sub-classes.

        Speaker: Rocco Lico (IRA/INAF and UniBO)
      • 6:15 PM
        MCMC estimation of SED model parameters using multi- wavelength data of the blazar Mrk 421 15m

        The spectral energy distributions (SEDs) of blazars are dominated by synchrotron and inverse Compton radiation. The origin of blazar variability can be investigated from the time variation of the SEDs. However, it is difficult to estimate the optimal model parameters of SEDs and their uncertainties because some parameters are strongly correlated and the standard method may be trapped by local solutions. In this study, we applied a Markov chain Monte Carlo method (MCMC) to this problem. Our experiments using artificial data demonstrate that at least one prior probability is required to uniquely determine the solution. We used simultaneous observations of Mrk 421 with Fermi-LAT, Swift-XRT, and the 1.5-m optical telescope, Kanata from 2009 to 2011 reported in Itoh et al. (2015). We succeeded in estimating the optimal parameters and their uncertainties by using the prior probability of the time-scale and Doppler factor. As a result, we found that the break energy of electron energy distribution is proportional to X-ray flux and the normalization of electron distribution is inversely proportional. These correlations suggest that the X-ray variations were caused by the fluctuations of the break energy rather than the number of electrons.

        Speaker: Yurika Yamada (Hiroshima University)
    • 5:00 PM 6:30 PM
      Central Galaxy GaPa/1-1 - Olympiasaal (Garmisch-Partenkirchen)

      GaPa/1-1 - Olympiasaal


      Convener: Nir Shaviv (Hebrew University of Jerusalem)
      • 5:00 PM
        Galactic center GeV excess: status and interpretations 30m GaPa/1-1 - Olympiasaal

        GaPa/1-1 - Olympiasaal



        The Galactic center (GC) is one of the most important regions to search for a gamma-ray signal from a possible annihilation of dark matter due to its proximity and high dark matter density. In the past years, several groups have reported an excess of gamma rays in the Fermi-LAT data with an approximately spherical morphology around the GC. In this talk I will review the current observational status of the excess, the difficulties in the gamma-ray analysis near the GC, and possible interpretations, such as an additional source of cosmic rays, a population of millisecond pulsars, and dark matter annihilation. I will discuss how one can distinguish these possibilities with future observations.

        Speaker: Dmitry Malyshev (ECAP)
      • 5:30 PM
        Modeling the Galactic Center Gamma-Ray Excess 30m GaPa/1-1 - Olympiasaal

        GaPa/1-1 - Olympiasaal



        Over the last seven years, Fermi-LAT observations have convincingly
        found an excess in gamma-ray emission emanating from the center of the
        Milky Way galaxy. The excess has three definitive properties: (1) it
        has a hard spectrum that peaks at an energy of ~2 GeV, (2) it extends
        from within 0.1 degrees to more than 10 degrees from Sgr A* with a
        three-dimensional intensity that falls roughly as r^-2, (3) it is
        approximately spherically symmetric. Several models for this excess
        have been formulated, including the collective emission from a
        population of individually dim gamma-ray pulsars, outbursts of
        cosmic-ray electrons from the central molecular zone, or potentially
        even dark matter annihilation. In this talk, I will discuss the
        arguments for and against each model, focusing specifically on
        constraints from multi-wavelength observations. Additionally, I will
        discuss the future observations that are critical for understanding
        the origin of the gamma-ray excess.

        Speaker: Tim Linden
      • 6:00 PM
        Is the Galactic Centre Excess due to the X-shaped stellar over-density in the Galactic bulge? 15m GaPa/1-1 - Olympiasaal

        GaPa/1-1 - Olympiasaal



        An anomalous excess emission has been found in Fermi-LAT data covering the centre of the Galaxy. We report on an analysis that exploits hydrodynamical modelling to register the position of interstellar gas associated with diffuse Galactic gamma-ray emission. Our analysis reveals that the excess gamma rays’ morphology is statistically well described by the X-shaped stellar over-density in the Galactic bulge and the nuclear stellar bulge. Given the non-spherical nature of these over-densities, we argue that the GCE is not a dark matter phenomenon but may rather be associated with the stellar population of the bulge and the nuclear bulge.

        Speaker: Chris Gordon (University of Canterbury)
      • 6:15 PM
        Monitoring the Galactic Center with MAGIC for more than 5 years 15m GaPa/1-1 - Olympiasaal

        GaPa/1-1 - Olympiasaal



        The Galactic Center (GC) region with its rich and dense astrophysical
        environment and a 4 million solar mass black hole (BH) at its center has
        always been one of the primary targets for observations with gamma-ray

        MAGIC has been observing the GC within a multi-year monitoring campaign
        since the first reports about the G2 fly-by in 2012. These observations
        have been carried out at large zenith angles, leading to a higher energy
        threshold but also to increased sensitivity at multi-TeV energies.

        I will present the results of the multi-year monitoring program of SgrA*
        with the MAGIC telescopes during the time period around and after the
        pericentre passage of the G2 object, where MAGIC did not detect any
        unusual variability, similar to what has been reported for other
        wavelengths. A detailed morphology study of the region, a significant
        by-product of the monitoring that became possible due to the
        availability of new Fermi tools inspired software for MAGIC data, allows
        us to revisit the properties of the GC diffuse emission that recently lead
        H.E.S.S. to claim the existence of a PeV cosmic ray source located at

        Speaker: Dr Christian Fruck (Max-Planck-Institut für Physik)
    • 8:30 AM 10:30 AM
      Transients and Gamma-Ray Bursts I: Gravitational Waves
      Convener: John Kirk (Max-Planck-Institut fuer Kernphysik)
      • 8:30 AM
        Gravitational Wave Astronomy with Advanced LIGO/Virgo 30m

        Observation of gravitational-waves from compact binary mergers with Advanced LIGO have opened up the field of gravitational-wave astronomy. We'll discuss results from
        the recent observing run of LIGO/Virgo and prospects for the future.

        Speaker: Alexander Nitz (Max Planck Institute for Gravitational Physics (Albert Einstein Institute))
      • 9:00 AM
        GBM results in the GW Era 30m

        We talk about the released results from the searches of GBM data for electromagnetic counterparts to gravitational waves.

        Speaker: Eric Burns (NASA GSFC/USRA)
      • 9:30 AM
        INTEGRAL follow-up of the gravitational wave events 15m

        We use observations of the INTErnational Gamma-Ray Astrophysics
        Laboratory (INTEGRAL) to search for gamma-ray and hard X-ray emission
        associated with the gravitational wave events discovered during the
        first and the second scientific runs of Advanced LIGO and Advanced
        Virgo. The highly eccentric orbit of INTEGRAL ensures high duty
        cycle, long-term stable background, and unobstructed view of nearly
        the entire sky. This enables us to use a combination of INTEGRAL
        instruments (SPI-ACS, IBIS/Veto, and IBIS) to search for a hard X-ray
        electromagnetic signal in the full high-probability sky region for
        almost every single LIGO trigger.

        The fraction of the energy promptly released in gamma-rays in 75 keV
        - 2 MeV energy range in the direction of the observer is constrained
        to be less than one millionth of the gravitational wave energy, in
        the majority of the localization region. Moreover, in the case of
        LVT151012 INTEGRAL high-energy imaging instruments, IBIS, SPI, and
        JEM-X, provided the unique opportunity to search also for
        long-lasting electromagnetic counterparts of this event over 3
        decades in energy, from 5 keV to 8 MeV.

        Speaker: Volodymyr Savchenko (University of Geneva)
      • 9:45 AM
        Follow-up of Gravitational Wave Events with the Fermi-LAT. Current Status and Prospects for the Future 15m

        As the first detections of Gravitational Waves (GW) from the coalescence of compact objects were announced by LIGO and Virgo, a new era for astronomy began. Searches for electromagnetic (EM) counterparts of GW events are of fundamental importance, as their success will increase the confidence in the GW detection and will help characterize the system parameters. The Fermi Gamma-ray Space Telescope is the most capable observatory to simultaneously observe a large fraction of the sky from 10 keV to more than 300 GeV, providing the unique capability of rapidly covering the entire probability region from a LIGO candidate. In this talk, I will present the strategy for follow-up observations of GW events with the Fermi Large Area Telescope (LAT), focusing on the results from the first science runs O1/O2. I will also discuss the prospects for detections of GW in coincidence with a gamma-ray signal from the Fermi Gamma-ray Burst Monitor (GBM) and the LAT, likely from a short Gamma-Ray Burst (sGRB) arising from the merger of two neutron stars.

        Speaker: Nicola Omodei
      • 10:00 AM
        Off-axis short GRBs from structured jets as counterparts to GW events 15m

        Binary neutron star mergers are considered to be the most favorable sources that produce electromagnetic (EM) signals associated with gravitational waves (GWs). They are also the likely progenitors of short duration gamma-ray bursts (GRBs). The brief gamma-ray emission (the “prompt” GRB emission) is produced by ultra-relativistic jets, as a result, this emission is strongly beamed over a small solid angle along the jet. It is estimated to be a decade or more before a short GRB jet within the LIGO volume points along our line of sight. For this reason, the study of the prompt signal as an EM counterpart to GW events has been largely ignored. We argue that for a realistic jet model, one whose luminosity and Lorentz factor vary smoothly with angle, the prompt signal can be detected for a significantly broader range of viewing angles. This can lead to a new type of EM counterpart, an “off-axis” short GRB. Our estimates and simulations show, that with the aid of the temporal coincidence from a LIGO trigger, it is feasible to detect these prompt signals with a detector such as Fermi, even if the observer is substantially misaligned with respect to the jet.

        Speaker: Adithan Kathirgamaraju (Purdue University)
      • 10:15 AM
        Analysing the light curve and spectra of the first detected kilonova 15m

        AT2017gfo is the first clearly detected kilonova, with comprehensive photometry and spectroscopy in the optical and NIR. I discuss this unique dataset in the context of previously published models and show fitting results using newly developed ones. I discuss inferred constraints on ejecta mass and composition in relation to simulations of neutron star mergers and theories for the origin of the r-process elements.

        Speaker: Anders Jerkstrand (MPI Astrophysik)
    • 10:30 AM 11:00 AM
      Break 30m
    • 11:00 AM 12:30 PM
      Stellar sources (galactic and extragalactic) I: Binaries
      Convener: Olaf Reimer (Universität Innsbruck)
      • 11:00 AM
        Recent multi-wavelength studies of gamma-ray binary hosting Be star 30m

        The gamma-ray binary is composed of the compact object (pulsar/black hole)
        and high mass OB star, and is gamma-ray loud object. In this talk, I will focus on recent theoretical and observational studies for the gamma-ray binary hosting Be star.

        For PSR B1259-63/LS 2883, the origin of flare-like GeV emission after the second disk passage is puzzling, and it may be interpreted as a consequence of the inverse-Compton process of the pulsar wind scattering off the soft photon from
        the accretion disk around the pulsar. For HESSJ0632+057,
        the recent optical/X-ray studies indicate a shorter
        orbital period and a smaller eccentricity than those reported
        in previous. Phase positions of the observed X-ray flare and dip
        are modified by new orbital parameters. PSR J2032+4127/MT91 213 is the candidate of the gamma-ray binary with a orbit period ~50 years. The X-ray flux from this system rapidly increases with flare-like activities, as the pulsar approaches to the periastron in late 2017/early 2018.
        I will also report new feature of the super orbital modulation of LS I +61$^{\circ}$303 using ~8 years Fermi-LAT data.

        Speaker: Jumpei Takata
      • 11:30 AM
        Fermi acceleration under control: $\eta$ Carinae 15m

        The $\eta$ Carinae binary system hosts a massive stars featuring the highest known mass-loss rate. The two colliding winds dissipate mechanical energy in the shock, accelerating particles up to relativistic energies, and producing high-energy $\gamma$-rays. We analysed Fermi LAT data over two full orbital periods, comparing them with the predictions of particle acceleration in hydrodynamic simulations. We detected two distinct emission components: a low-energy component cutting off below 10 GeV, with short-term variability at periastron; an high-energy component varying by a factor 4, but differently during the two periastrons. This suggest a modification of the wind density in the inner wind collision zone, confirmed also in X-ray. Observations match the prediction of the particle in cell simulations. CTA and e-Astrogam could help to understand/constrain acceleration physics in more extreme conditions than in SNR.

        Speaker: Matteo Balbo (University of Geneva)
      • 11:45 AM
        Gamma ray emission from Cyg X-3 and Cyg X-1 15m

        We studied gamma-ray emission from Cyg X-3 and Cyg X-1 with the LAT. With the currently improved calibration and background determination, we studied spectra and variability of Cyg X-3 in its soft, intermediate and hard states and during bright flares. We measured detailed spectra for all of the states except for finding upper limits only in the hard state, in spite of strong radio emission correlated with X-rays in that state. We also measured the orbital modulation to a much greater precision than before. We modelled the spectra and the modulation in terms of jet models and found strong constraints on the location of the bulk of the emission (at a distance along the jet comparable to the separation). The gamma-ray emission is strongly correlated with the radio, which allows us to measure the time lag.

        In the case of Cyg X-1, we determined a detailed LAT spectrum in the hard/intermediate state and found a significant soft excess below 60 MeV. Also, while we found no soft-state emission above 100 MeV, we found a significant flux below it. In both cases, the soft excesses connect to the previously measured MeV tails.

        Speaker: Andrzej Zdziarski (N. Copernicus Astronomical Center, Warsaw)
      • 12:00 PM
        Towards the emerging source class of γ-ray emitting colliding-wind binary systems 15m

        Recently published results using seven years of Fermi-LAT data shed new light on the still puzzling source class of particle-accelerating colliding-wind binary (CWB) systems.
        While the claimed association of the system $\gamma^2$ Velorum (WR 11) with a high-energy $\gamma$-ray source contrasts the exclusivity of $\eta$ Carinae as the hitherto only detected $\gamma$-ray emitter of that sort, the low upper limits obtained for WR 140 strengthen the question why this system with all its similarities to the $\gamma$-ray bright $\eta$ Carinae remains still unseen.

        We use three-dimensional magneto-hydrodynamic modeling (MHD) to investigate the structure and conditions of the wind-collision region (WCR) in these three systems, including the important effect of radiative braking in the stellar winds. A transport equation is then solved throughout the computational domain to study the propagation of relativistic electrons and protons. The resulting distributions of particles are subsequently used to compute nonthermal photon emission components.

        With the above procedure, we obtained first model results that can account for the weak detection of $\gamma^2$ Velorum, the strong detection of $\eta$ Carinae, and the non-detection of WR 140 in a similar computational setup.

        Speaker: Klaus Reitberger (Leopold-Franzens Universität Innsbruck)
      • 12:15 PM
        The population of gamma-ray binaries 15m

        Gamma-ray binaries, whose spectral energy distribution peaks above 1 MeV, are rare objects thought to be composed of a pulsar in orbit around a massive star. How many gamma-ray binaries are there in the Galaxy ? What are the prospects for detecting them ? We have carried out mock gamma-ray surveys of synthetic populations of gamma-ray binaries to answer these questions.

        Speaker: Guillaume Dubus (CNRS)
    • 12:30 PM 2:00 PM
      Catered Lunch 1h 30m
    • 2:00 PM 3:45 PM
      Stellar sources (galactic and extragalactic) II GaPa/1-1 - Olympiasaal (Garmisch-Partenkirchen)

      GaPa/1-1 - Olympiasaal


      Convener: Andrzej Zdziarski (N. Copernicus Astronomical Center, Warsaw)
      • 2:00 PM
        The Gamma-ray Binary in the LMC: Implications for Populations and Further Discoveries 30m

        Gamma-ray binaries, systems containing interacting compact objects whose radiative output is dominated by gamma-ray emission, are evolutionary precursors of high-mass X-ray binaries, and tens of these objects had been predicted to exist in our Galaxy. We have been searching for new members of this class via the detection of periodic modulation of LAT light curves, with extensive multi-wavelength followup. After our early discovery of 1FGL J1018.6-5856, no additional source had been found until our identification of LMC P3 as another binary, the first gamma-ray binary outside the Milky Way. We present our search techniques, illustrated by the LMC P3 discovery, discuss the implications for the population of gamma-ray binaries and possible future discoveries, and describe our continued observations of the known binaries to better understand their properties and astrophysics.

        Speaker: Robin Corbet
      • 2:30 PM
        The Monster Next Door: Fermi-LAT observations of Supernova Remnant N132D in the Large Magellanic Cloud 15m

        Supernova remnant (SNR) N132D, located in the Large Magellanic Cloud, represents a unique opportunity for the study of gamma-ray emission from shock-accelerated cosmic rays (CRs) in another galaxy since it stands as the first and only extra-galactic SNR detected in gamma-rays. N132D is one of the brightest SNRs in the local Universe in the X-ray, infrared and radio bands, and it has also been detected in TeV energy gamma-rays. N132D's apparent interaction with a giant molecular cloud strongly favors the scenario where the gamma-ray emission results from CR hadrons interacting with dense ambient media. We report on the detection of N132D with the Fermi-LAT, and by characterizing its emission in the MeV-GeV band, as well as constraining the non-thermal contribution to the X-ray spectrum using Chandra observations, we build a very complete picture of the properties of the system and its progenitor, ultimately helping us better understand CR acceleration in SNRs.

        Speaker: Daniel Castro (Harvard-Smithsonian Center for Astrophysics)
      • 2:45 PM
        Detection of SN 1006 and HESS J1731-347 with Fermi-LAT: a complete view of shell-type TeV SNRs 15m

        SNRs are considered to be the main sites in the Milky Way for producing cosmic rays with energies up to a few 10^15 eV. Among them, shell-like SNRs exhibit a morphology spatially coincident with the shock front of the SNR and are of great interest in the context of particle acceleration. Their common characteristics are a young age, a large angular size and TeV emission highly correlated with X-ray synchrotron emission.
        I will report the GeV gamma-ray detections of the shell-type SNRs HESS J1731−347 and SN 1006 using 8 years of Fermi-LAT Pass 8 data. Overall, the hard spectra of these SNRs suggest a common scenario in which the bulk of the gamma-ray emission is produced by inverse Compton scattering of high energy electrons. However, this does not rule out efficient hadron acceleration in these TeV shells and the spectral slope asymmetry visible in the case of SN 1006 might be a first evidence in this respect. These results will be compared with the 3 other TeV shell-type SNRs providing a first complete census of this class of source at gamma-ray energies.

        Speaker: Marianne LEMOINE-GOUMARD (CENBG - CNRS/IN2P3)
      • 3:00 PM
        Fermi Large Area Telescope observations of supernova remnants Kes 73 and Kes 79 15m

        The supernova remnants Kes 73 and Kes 79 can deposit a large amount of energy to their surroundings and are potentially responsible for particle acceleration. Using the data taken with the Fermi Large Area Telescope (LAT), we confirmed the presence of extended sources which are spatially associated with these two supernova remnants. Kes 73 shows intense emission from 100 MeV to $>$100 GeV, and its LAT spectrum can be decoupled into two components. According to the young age of the Kes 73 system, the observed $<$10 GeV flux is too high for the supernova remnant to account for, while the supernova remnant is reasonably responsible for the hard spectrum above 10 GeV. In the LAT spectrum of Kes 79, we discovered a genuine turnover (a sharp peak) at a photon energy of $290\pm26$ MeV, above which the spectrum follows a power-law with a photon index of $2.63 \pm 0.05$. This peak is consistent with the scenario of proton-proton collision. The molecular clouds illuminated by hadronic cosmic-rays from Kes 79 is preferably dominating the $\gamma$-rays observed in this field.

        Speaker: Paul Kin-Hang YEUNG (Department of Physics, University of Hamburg)
      • 3:15 PM
        Disentangling hadronic from leptonic emission in the composite SNR G326.3-1.8 15m

        Supernova remnants (SNRs), pulsar wind nebulae (PWNe) and pulsars are the usual suspects to accelerate the bulk of cosmic rays in our Galaxy. In those objects the gamma-ray emission allows us to probe the population of high-energy particles and in particular the population of accelerated hadrons radiating through the pion-decay mechanism. In case of composite SNRs, both the SNR shell and the PWN are sometimes bright enough to be observed in the same source. However, understanding the nature of the gamma-ray emission in such objects can be challenging for sources of small angular extent. Previous studies of the composite SNR G326.3-1.8 (radius=0.3°) revealed bright and extended gamma-ray emission but its origin remained uncertain.
        With the recent Pass8 Fermi-LAT data that provide an increased acceptance and angular resolution, we investigate the morphology of this source to disentangle the PWN from the SNR contributions. In particular, we take advantage of the new possibility to filter events based on their angular reconstruction quality (PSF types). We also report a spectral analysis and derive some physical properties using one-zone models for the SNR spectrum.

        Speaker: Justine Devin (CNRS/IN2P3 - Laboratoire Univers et Particules de Montpellier)
      • 3:30 PM
        Thermal X-ray studies on escaping of accelerated protons from SNR shocks 15m

        A number of middle-aged SNRs with molecular clouds (MCs) emit GeV gamma-rays originating from accelerated protons. About half of GeV SNRs also have recombining plasma (RP; the plasma with ionization temperatures that are higher than electron temperatures), implying rapid cooling of the electrons. These facts indicate thermal plasma can be the key to understand the escaping process of accelerated protons from SNR shocks.
        We have made thermal X-ray study of the GeV SNR HB 21. HB 21 is interacting with MCs and the faintest in GeV band among GeV SNRs. We discovered a strong radiative recombination continuum of Si from the center of the remnant, which is the direct evidence of RP (electron temperature of $0.16\pm0.01$ keV and recombination timescale of $(2.8\pm0.5)\times10^{11}$ s cm$^{-3}$).
        The estimated RP age ($\sim100$ kyr) is the longest among GeV SNRs with RP.
        Systematic study of GeV SNRs shows a strong correlation between RP age and photon index in the GeV band.
        It supports the following scenario; interaction with MCs makes a magnetic field partially weaker and protons escape, simultaneously cooling down the SNR plasma to be recombining.

        Speaker: Mr Hiromasa Suzuki (University of Tokyo)
    • 2:00 PM 3:45 PM
      Transients and Gamma-Ray Bursts II: Gamma-Ray Bursts GaPa/2-1 - Konzertsaal (Garmisch-Partenkirchen)

      GaPa/2-1 - Konzertsaal


      Convener: Markus Boettcher (North-West University)
      • 2:00 PM
        Emission from accelerating jets in gamma-ray bursts: Radiation dominated flows with increasing mass outflow rates 15m

        We study the narrowest spectra expected from GRBs. We present an analytical function for the spectrum that is emitted from the photosphere of a radiation-dominated flow that is under acceleration. We also present numerical spectra from photospheres occurring during the transition into the coasting phase of the flow. Using these spectral models, we reanalyse Fermi observations of GRB100507 and GRB101219, which both have been reported to have very narrow spectra. The bursts can be fitted by the spectral models: For GRB101219 the spectrum is consistent with the photosphere occurring below or close to the saturation radius, while for GRB100507 the photosphere position relative to the saturation radius can be determined as a function of time. In the latter case, we find that the photosphere initially occurs in the acceleration phase and thereafter transitions into the coasting phase. We also find that this transition occurs at the same time as the change in observed cooling behaviour: the temperature is close to constant before the break and decays after. We argue that such a transition can be explained by an increasing mass outflow rate. Both analysed bursts thus give strong evidence that the jets are initially radiation dominated.

        Speaker: Felix Ryde (Dept of Physics)
      • 2:15 PM
        GRB Locations and Spectra with the BALROG 15m

        In the era of multi-messenger astronomy, all-sky surveys of transient events serve an important role to provide detection and location information to follow-up instruments. The Fermi-GBM serves as the dominant gamma-ray transient detector with coverage of the entire unocculted sky. We introduce a new method to improve both the precision and accuracy of the Fermi-GBM’s ability to locate gamma-ray transients. The method been shown to improve the previously reported systematics of the official localization method. I will discuss the issues with localization, how the method attempts to overcome them, and the still existing problems that must be overcome to provide accurate and precise localizations. These efforts are vital for gravitational wave follow-up. Additionally, I will discuss the impact of our localization method on observed GRB spectra and argue that we still have a long path to fully understanding the spectra before making accurate physical inferences about them.

        Speaker: J. Michael Burgess (Max-Planck-Institut für extraterrestrische Physik)
      • 2:30 PM
        The Konus-Wind catalog of gamma-ray bursts with known redshifts. I. Bursts detected in the triggered mode. 15m

        In this catalog, we present the results of a systematic study of 150 gamma-ray bursts (GRBs) with reliable redshift estimates detected in the triggered mode of the Konus-Wind (KW) experiment. The sample covers the period from 1997 February to 2016 June and represents the largest set of cosmological GRBs studied to date over a broad energy band. We provide the burst durations, the spectral lags, the results of spectral fits with two model functions, the total energy fluences, and the peak energy fluxes, the rest-frame, isotropic-equivalent energy and peak luminosity, the collimation-corrected values of the energetics for 32 GRBs with reasonably-constrained jet breaks. We consider the behavior of the rest-frame GRB parameters in the hardness-duration and hardness-intensity planes, and confirm the ’Amati’ and ’Yonetoku’ relations for Type II GRBs. The correction for the jet collimation does not improve these correlations for the KW sample. We discuss the influence of instrumental selection effects on the GRB parameter distributions and estimate the KW GRB detection horizon. Accounting for the instrumental bias, we estimate the KW GRB luminosity evolution, luminosity and isotropic-energy functions, and the evolution of the GRB formation rate.

        Speaker: Ms Anastasia Tsvetkova (Ioffe Institute)
      • 2:45 PM
        Exploring the low-energy domain of LAT-detected GRBs id 18440 15m

        In preparation for the Second LAT Gamma-Ray Burst (GRB) catalog, we explore the use
        of the LAT low-energy (LLE) data selection to detect bursts with gamma-ray energy below 100 MeV. Here we present the sample of GRBs that are detected at these energies
        through a Bayesian Block analysis of all Fermi Gamma-ray Burst Monitor (GBM)
        triggers collected in 8 years of Fermi mission.
        In particular, we compare the temporal characteristics of this sample of GRBs
        with those of the brightest bursts detected above 1 MeV by the GBM.
        Finally, we examine the properties of a subset of events
        which are not detected above 100 MeV (LLE-only GRBs).

        Speaker: Elisabetta Bissaldi (Politecnico & INFN Bari)
      • 3:00 PM
        The Bright and the Slow - GRBs 100724B and 160509A with high-energy cutoffs at < 100MeV 15m

        We analyze the prompt emission of two of the brightest Gamma-Ray Bursts (GRBs) observed by Fermi at MeV energies but surprisingly faint at > 100 MeV energies. Time-resolved spectroscopy reveals a sharp high-energy cutoff. We first characterize phenomenologically the cutoff and its time evolution. We then fit the data to two models where the high-energy cutoff arises from intrinsic opacity to pair production within the source. Alternative explanations for the cutoff, such as an intrinsic cutoff in the emitting electron energy distribution, appear to be less natural. Both models provide a good fit to the data with very reasonable physical parameters, providing a direct estimate of bulk Lorentz factors on the lower end of what is generally observed in Fermi GRBs. Surprisingly, their lower cutoff energies Ec compared to other Fermi-LAT GRBs arise not predominantly from the lower Lorentz factors, but also at a comparable level from differences in variability time, luminosity, and high-energy photon index. Finally, particularly low Ec values may prevent detection by Fermi-LAT, thus introducing a bias in the Fermi-LAT GRB sample against GRBs with low Lorentz factors or variability times.

        Speaker: Giacomo Vianello (Stanford University)
      • 3:15 PM
        Magnetic versus baryonic jets for gamma-ray bursts. 15m

        The magnetization of gamma-ray burst jets is one of the most important unanswered questions to-date, as it would help to constrain the progenitor, the emission mechanism(s) and the central engine of GRBs. In my talk, I explain how observables can set constraints on models of magnetized jets in the framework of photospheric emission.

        Speaker: Damien Begue (MPE)
      • 3:30 PM
        Constraints on microphysical parameters of GRBs using HAWC 15m

        The physical mechanism at the origin of gamma-ray bursts (GRBs) is far from being completely understood. Describing their emission up to very high energies (GeV-TeV) is one of the most challenging and important tasks needed to unveil the physics of these peculiar events.
        Using data collected by the HAWC gamma-ray observatory, we search for TeV emission coming from a sample of GRBs detected by Fermi and Swift between December 2014 and May 2017. We derive upper limits derived over different time intervals and use them to constrain the microphysical parameters and the bulk Lorentz factor under the assumption of the external shock model scenario. We present the results of this analysis discussing possible interpretations.

        Speaker: Simone Dichiara (Universidad Nacional Autónoma de México)
    • 3:45 PM 4:15 PM
      Coffee Break 30m
    • 4:15 PM 6:00 PM
      Stellar sources (galactic and extragalactic) III GaPa/1-1 - Olympiasaal (Garmisch-Partenkirchen)

      GaPa/1-1 - Olympiasaal


      Convener: Martin Pohl (Universität Potsdam)
      • 4:15 PM
        New Extended GeV Sources in the Galactic Plane Found using 6 years of Fermi-LAT Pass 8 data 15m

        Spatially resolving pulsar wind nebulae (PWNe) and supernova remnants (SNRs) at GeV energies enables accurate representation of spectra, aids identification of multiwavelength counterparts, and probes possible substructure within the gamma-ray sources. Using 6 years of Fermi-LAT Pass 8 data above 10 GeV, we searched for spatially extended sources near the Galactic plane. The improved angular resolution and photon acceptance of the Pass 8 event reconstruction significantly aids in characterizing source extension and assessing spectral and morphological properties, a key consideration for studies of PWNe and SNRs in the gamma-ray band. Selecting photons above 10 GeV strikes a balance between keeping photon statistics high and diffuse gamma-ray emission low, and also carries the benefit of a near constancy with energy of the point spread function of the LAT. More than 30 significantly extended sources are detected, more than a dozen of which are resolved at GeV energies for the first time.

        Speaker: Marie-Hélène Grondin (CENBG, Université de Bordeaux/CNRS-IN2P3)
      • 4:30 PM
        Resolving the Crab Nebula in TeV gamma-rays with H.E.S.S. 15m

        Although the Crab Nebula is one of the best-studied astrophysical sources, its extension in gamma-rays remained unknown until now. Measuring the size of the Crab Nebula in very high energy (VHE) gamma-rays provides important input on understanding the physics of this quite unusual pulsar wind nebula. The suspected extension is well below the angular resolution of Imaging Atmospheric Cherenkov Telescopes, which makes a good understanding of the instrument point spread function (PSF) indispensable. The PSF depends strongly on the observation and instrument conditions, demanding time-dependent simulations of these. Utilising such simulations, the point-source resolvability in VHE gamma-ray astronomy has now been pushed to a new level by H.E.S.S., allowing to probe source extensions well below one arcminute scale. This enables us to reveal the extension of the Crab Nebula in VHE gamma-rays for the first time. Assuming a Gaussian source shape, we obtain a width of 52’’.

        Speaker: Markus Holler (Universität Innsbruck)
      • 4:45 PM
        On the origin of gamma-ray emission toward SNR CTB 37A with Fermi-LAT 15m

        Supernova remnants (SNRs) are believed to be one of the major sources of Galactic cosmic rays. SNR CTB 37A is known to interact with several dense molecular clouds as traced by OH 1720 MHz maser. Radio and X-ray observations of the SNR confirm a mixed-morphology classification of the remnant. The TeV γ-ray source HESS J1714-385 is positionally coincident with the SNR, though it is still not clear whether the TeV γ-ray emission originates in the SNR or in a plausible pulsar wind nebula (PWN). In the present work, we use 8 years of Pass 8 Fermi-LAT data, with high capability to resolve γ-ray sources, to perform morphological and spectral studies of the γ- ray emission toward CTB 37A from 200 MeV to 200 GeV. The best fit of the source extension is obtained for a Gaussian model of 68% containment radius 0.18° ± 0.02°. We also discuss several possible theoretical models to explain the broadband spectrum and to elucidate the nature of the high-energy γ-ray emission toward CTB 37A.

        Speaker: Soheila Abdollahi (Hiroshima University)
      • 5:00 PM
        Similarity of $\gamma$-ray spectrum in middle aged supernova remnants interacting with molecular clouds: what can we learn? 15m

        We compare the $\gamma$-ray spectrum available in literature from middle aged supernova remnants (SNRs) interacting with molecular clouds (MCs). We demonstrate the similarity in the shape of $\gamma$-ray spectra and then clarify a few points about the $\pi^0$-decay signatures claimed in a few SNRs. Next, we discuss the escaping scenario and direct interaction scenario, which have been proposed to interpret the observed $\gamma$-ray emission. We show that the similarity presented in $\gamma$-ray spectra is inconsistent with the prediction from escaping scenario statistically. It may imply that the widely used free escape boundary is not a good prescription to study escaping CRs and illuminated MCs. In the direct interaction scenario involving re-acceleration of pre-existing CRs, the similarity in $\gamma$-ray spectra can be understood as a reflection of almost uniform CR background in our Galaxy. However, the model suggests a transition in seed particles for diffusive shock acceleration during the SNR evolution. Whether such transition indeed exists and how does it affect SNRs’ contribution to Galactic CRs have to be investigated by future observation and theoretical modeling. In the end, we discuss the contribution of SNRs to the Galactic diffuse $\gamma$-ray emission.

        Speaker: Xiaping Tang (Max Planck Institute for Astrophysics)
      • 5:15 PM
        Diffusive shock acceleration in the young supernova remnant G1.9+0.3 15m

        The very young Supernova remnant G1.9+0.3 is an interesting target for next generation gamma-ray observatories. So far the remnant is only detected in the radio and the X-ray bands but its young age and inferred shock speed of 14,000km/s should make it an efficient particle accelerator.
        We carry out spherical symmetric 1-D simulations where we simultaneously solve the transport equations for the cosmic rays and the hydrodynamical flow using the PATRON code. With our test-particle simulations we are able to reproduce the observed radio and x-ray spectra together with the radio and x-ray profiles in the east-west direction and the observed radio-flux increase of about 1.2%/yr.

        Speaker: Robert Brose
      • 5:30 PM
        A New Gamma-Ray Source in the Vicinity of the Galactic Supernova Remnant G306.3−0.9 15m

        A new extended gamma-ray source, which was named as ‘SourceA’, in the southwest of Galactic supernova remnant (SNR) G306.3−0.9 was detected with a significance of ~13σ at the location of R.A.(J2000) = 199.47 deg ± 0.07 deg and decl.(J2000) = −63.93 deg ± 0.07 deg using about 9 years of Fermi−LAT data. Showing the properties and detectability levels of non-TeV pulsar wind nebulae (PWNe), SourceA might be a PWN. In order to investigate this unidentified gamma-ray source in multi-wavelengths, we performed Swift observations of SourceA. In this presentation we will summarize the published gamma-ray results, report on the Swift observations, and show our preliminary results of the gamma-ray variability analysis of SourceA.

        Speaker: Tulun Ergin (TUBITAK Space Technologies Research Institute)
    • 4:15 PM 6:00 PM
      Transients and Gamma-Ray Bursts III: Radio Transients and Novae GaPa/2-1 - Konzertsaal (Garmisch-Partenkirchen)

      GaPa/2-1 - Konzertsaal


      Convener: Guillaume Dubus (CNRS IPAG)
      • 4:15 PM
        Fast Radio Bursts - implications for Fermi and future prospects 30m

        Radio astronomy is currently exploring an intriguing new phase space that probes the
        dynamic Universe on timescales of milliseconds. Recent development of sensitive, high time
        resolution instruments has enabled the discovery of millisecond duration fast radio bursts
        (FRBs). The FRB class encompasses a number of single pulses, each unique in its own way, hindering a consensus for their origin. The key to demystifying FRBs lies in discovering many of them in realtime in order to identity commonalities. Despite rigorous follow-up at radio and other wavelengths, with the exception of the FRB discovered by the Arecibo telescope, none of the other FRBs have been seen to repeat suggesting the possibility of there existing two independent classes of FRBs with two classes of possible progenitors. In my talk I will present an overview of the FRB population and their implications for Fermi and the future prospects of the field.

        Speaker: Manisha Caleb (University of Manchester)
      • 4:45 PM
        Probing mass ejection in nova outbursts using gamma-rays 15m

        Thanks to the Fermi Large Area Telescope (LAT), novae have been established as a new class of particle accelerators and gamma-ray emitters, with 9 objects detected as transient GeV sources so far. A possible origin for this non-thermal emission is internal shocks in the nova ejecta, resulting from the interaction of a fast wind radiatively-driven by nuclear burning on the white dwarf with material ejected in the initial runaway stage of the outburst.
        We present a model for the dynamics of such internal shocks and for the associated diffusive shock acceleration and high-energy emission. Non-thermal proton and electron spectra are calculated by solving a time-dependent transport equation for particle injection, acceleration, losses, and escape from the shock region. Predicted spectra and lightcurves are fitted to observations of the first 6 novae detected by the LAT to derive the properties of the nova outbursts. From these results, we discuss the potential of gamma-rays for probing the mechanism of mass ejection in novae in conjunction with diagnostics of the thermal emission.

        Speaker: Dr Pierrick Martin (CNRS/IRAP)
      • 5:00 PM
        Gamma-ray Novae: Rare or Nearby? 15m

        Classical Novae were revealed as a surprise source of gamma-rays in Fermi LAT observations. During the first 8 years since the LAT was launched, 6 novae in total have been detected to > 5 sigma in gamma-rays, in contrast to the 69 discovered optically in the same period. We attempt to resolve this discrepancy by assuming all novae are gamma-ray emitters, with peak one-day fluxes consistent to those observed. To determine optical parameters, the spatial distribution and magnitudes of bulge and disc novae in M31 are scaled to the Milky Way. We approximate Galactic reddening using a double exponential disc with vertical and radial scale heights of r_d = 5 kpc and z_d = 0.2 kpc, and demonstrate that even such a rudimentary model can easily reproduce the observed fraction of gamma-ray novae, implying that these apparently rare sources are in fact nearby and not intrinsically rare. We conclude that classical novae with m_R < 12 and within ~8 kpc are likely to be discovered in gamma-rays using the Fermi LAT.

        Speaker: Paul Morris (University of Oxford)
      • 5:15 PM
        Classical Novae in the Age of Fermi 15m

        One of the great surprises from the Fermi Gamma-ray Space Telescope is the discovery that classical novae are sources of GeV gamma-ray emission. Despite the low velocities (~few thousand km/s) and low masses (~$10^{-5}$ solar masses) of their ejecta, these explosions still manage to produce populations of relativistic particles. The ENova team studies classical novae at all available wavelengths. Here, we present new discoveries from our observations with the Karl G. Jansky Very Large Array (VLA), the Hubble Space Telescope (HST), Swift, Chandra, NuSTAR, and (of course) Fermi. Fermi and optical monitoring uncover correlation between the optical and gamma-ray light curves, indicating the optical light is reprocessed emission from shocks and favoring the hadronic model for gamma-ray emission. Swift and VLA monitoring reveal evidence for multiple shocks in some novae. HST and VLA imaging point to a misalignment between optical and radio structures in at least one nova. NuSTAR observations provide new information about the hard X-ray regime, beginning to fill in the previously un-observable gap between Swift/Chandra and Fermi. Exciting new projects are underway or planned on all of these instruments.

        Speaker: Justin Linford (The George Washington University)
    • 8:30 AM 10:30 AM
      GeV to TeV
      Convener: Andy Strong
      • 8:30 AM
        Gamma-ray astronomy across 6 decades of energy: synergy between Fermi, IACTs, and HAWC observatories 30m

        Gamma-ray astronomy currently has an unprecedented sensitivity with instruments covering 6 decades of energy from 100MeV to 100TeV. The surveying capability at complementary energies between Fermi and HAWC allows extensive coverage for transients and flares. Very extended emissions are also being revealed within our Galaxy from nearby pulsar wind nebulae and star-forming regions. Using these HAWC and Fermi discoveries as targets, the finer resolution of imaging telescopes can begin to deconvolve the morphology of complex regions and follow up on sources found in previously unsurveyed regions with deeper exposures. With all these instruments in operation, the gamma-ray field is well-poised for multi-wavelength and multi-messenger astronomy.

        Speaker: Michelle Hui (NASA/MSFC)
      • 9:00 AM
        H.E.S.S. highlights 30m

        H.E.S.S. highlights

        The H.E.S.S. collaboration continues to run an array of meanwhile five Imaging Atmospheric Cherenkov Telescopes to observe the Southern sky in TeV gamma-rays. In this presentation, I will review recent highlight results obtained with H.E.S.S., including the corresponding multiwavelength perspective and future prospects.

        Speaker: Gerd Puehlhofer (IAAT, University of Tuebingen)
      • 9:30 AM
        Highlights of VERITAS observations of extragalactic objects 15m

        VERITAS is one of the world’s most sensitive detectors of astrophysical VHE (E > 100 GeV) gamma rays, and nearly 5000 hours of observations have been targeted on active galactic nuclei (AGN) and other extragalactic objects. These studies of blazars, radio galaxies, and starburst galaxies have resulted in 37 detections, in most cases accompanied by contemporaneous, broadband observations, which enable detailed studies of the underlying physical processes. Recent highlights from the VERITAS observation program of extragalactic sources will be presented, including studies of the extragalactic background light and reports on the sources OJ287, BL Lacertae, and 1ES 1959+650.

        Speaker: Martin Pohl (Universität Potsdam)
      • 9:45 AM
        Recent Galactic Science Results from VERITAS on Pulsar Searches, PSR J2032+4127, and HAWC Follow-Ups 15m

        VERITAS is a ground-based imaging atmospheric Cherenkov telescope array sensitive to very high energy (VHE, E > 100 GeV) gamma rays. VERITAS has detected VHE gamma-ray emission from nearly 60 astrophysical sources of varied source classes. One of the primary areas of research of VERITAS is the study of galactic particle accelerators, and among the classes of galactic objects investigated are pulsars, binary systems, and pulsar wind nebulae. In this contribution, recent results from VERITAS on the three aforementioned source classes will be presented, including: results from a search for pulsed emission from 14 young pulsars appearing in archival VERITAS data; observations of the binary system PSR J2032+4127/MT91 213, which is quickly approaching its periastron passage set to occur in November 2017; and follow-up observations of new VHE gamma-ray sources detected by the HAWC observatory. These VERITAS observations will provide insight into the particle acceleration and radiation mechanisms at work in these galactic objects.

        Speaker: Gregory Richards
      • 10:00 AM
        Improved IGMF limits from Fermi and MAGIC observations of 1ES 0229+200 15m

        The existence of the Intergalactic Magnetic Field (IGMF) in the voids of the Large Scale Structure provides a unique opportunity to infer the information about the evolution of the Universe in the early times. Currently, the most promising way to measure this field is through the IGMF-induced halos around the distant, gamma-ray loud AGNs. Among these 1ES 0229+200 remains the most suitable, given its hard GeV spectrum and absence of strong variability on the yearly time scales.

        In what follows, we present the results of 4 years of MAGIC observations of 1ES 0229+200, combined with the 9 year of the Fermi/LAT data, aimed to detect the degree-scale IGMF-induced halo around this source in the GeV-TeV energy range. Though no halo is detected, these observations allow us to derive a lower bound on the IGMF strength (in the large correlation length limit) at the level of $10^{-14}$ G - combining both the morphological and spectral information on the halo. We further discuss the implications of this bound for the existing IGMF models.

        Speaker: Dr Ievgen Vovk (Max Planck Institute for Physics)
      • 10:15 AM
        Evidence for cosmic ray escape: the GeV to TeV morphology of the $\gamma$-Cygni SNR with MAGIC and Fermi-$\textit{LAT}$ 15m

        Until today the supernova remnant (SNR) paradigm provides the most plausible hypothesis for the origin of galactic cosmic rays. In contrast to the acceleration process, the way how cosmic rays are released into the interstellar medium is not well understood yet, partially due to the lack of observational signatures. Such a signature could be provided by gamma-rays produced in the interaction of escaping particles with the material surrounding the SNR.

        The middle-aged (~7000 years old) $\gamma$-Cygni SNR (G78.2+2.1) situated in the dense Cygnus region may be in the right evolutionary phase to study the leakage of cosmic rays into the ISM. The high-energy observations by VERITAS and Fermi-$\textit{LAT}$ revealed a complex, energy-dependent morphology of the SNR in the GeV-TeV band, different from that observed in X-rays.

        We present recent, deeper observations of the $\gamma$-Cygni region with the MAGIC telescopes. Combined with 8 years of Fermi-$\textit{LAT}$ data, we find clear evidences for the release of cosmic rays at northern part of the SNR shell. We further discuss these results in the context of the current understanding of cosmic ray escape scenarios.

        Speaker: Mr Marcel C. Strzys (Max Planck Institute for Physics)
    • 10:30 AM 11:00 AM
      Break 30m
    • 11:00 AM 12:30 PM
      Analysis techniques: Methods
      Convener: J. Michael Burgess (Max-Planck-Institut für extraterrestrische Physik)
      • 11:00 AM
        Information field theory for gamma ray astronomy 30m

        Imaging, the process of converting data into images, is in general an ill-posed problem that requires regularization by additional information. Information field theory (IFT) provides a consistent framework to fuse measurement data and abstract knowledge on signal fields into an optimal image by using field theoretical methods in Bayesian inference. Here, the IFT based D$^3$PO algorithm will be introduced, and its application to Fermi and RXTE data presented. The future vision of an Unified Bayesian Imaging tooKIT (UBIK) for multi-dimensional and multi-instrumental imaging and the first steps towards it will be presented.

        Speaker: Torsten Ensslin (MPI for Astrophysics)
      • 11:30 AM
        Searches for Angular Extension in High-Latitude Fermi-LAT Sources 15m

        We report on the Fermi High-Latitude Extended Source Catalog (FHES), a systematic search for spatial extension of gamma-ray sources reported in the Fermi Large Area Telescope (LAT) 3FGL and 3FHL catalogs at Galactic latitudes |b| > 5 degrees. While the majority of high-latitude LAT sources are extragalactic blazars that appear point-like within the LAT angular resolution, there are several physics scenarios that predict the existence of populations of spatially extended sources. If dark matter consists of weakly interacting massive particles, the annihilation or decay of these particles in subhalos of the Milky Way would appear as a population of unassociated gamma-ray sources with finite angular extent. Gamma-ray emission from blazars could also be extended (so-called pair halos) due to the deflection of electron-positron pairs in the intergalactic magnetic field (IGMF). Measurement of pair halos would constrain the strength and coherence length scale of the IGMF. We report on new extended source candidates and their associations found in the FHES as well as limits on the IGMF based on the non-observation of the cascade.

        Speaker: Regina Caputo (UMD/NASA/GSFC)
      • 11:45 AM
        A new way of searching for transients: the ADWO method and its results 15m

        With the detection of gravitational wave emissions from from merging compact objects, it is now more important than ever to effectively mine the data-set of gamma-satellites for non-triggered, short-duration transients. Hence we developed a new method called the Automatized Detector Weight Optimization (ADWO), applicable for space-borne detectors such as Fermi' GBM and RHESSI' ACS. Provided that the trigger time of an astrophysical event is well known (as in the case of a gravitational wave detection) but the detector response matrix is uncertain, ADWO combines the data of all detectors and energy channels to provide the best signal-to-noise ratio. We used ADWO to successfully identify any potential electromagnetic counterpart of gravitational wave events, as well as to detect previously un-triggered short-duration GRBs in the data-sets.

        Speaker: Zsolt Bagoly (Eotvos University)
      • 12:00 PM
        Time Domain Astronomy with Fermi GBM in the Multi-messenger Era 15m

        As the Multi-Messenger era begins with detections of gravitational waves with LIGO and neutrinos with IceCube,Fermi GBM provides context observations of gamma-ray transients between 8 keV and 40 MeV. GBM has a wide field of view, high uptime, and both in-orbit triggering and high time resolution continuous data enabling offline searches for weaker transients. GBM detects numerous GRBs, SGRs, X-ray bursters, solar flares and TGFs. Longer timescale transients, predominantly in our galaxy so far, are detected using the Earth occultation technique and epoch-folding for periodic sources. The GBM team has developed two ground-based searches to enhance detections of faint transients, especially short GRBs. The targeted search uses the time and location of an event detected with another instrument to coherently search the GBM data, increasing the sensitivity to a transient. The untargeted search agnostically searches the GBM data for all directions and times to find weaker transients. This search finds ~80 short GRBs per year, in addition to the 40 per year triggered on-orbit. With its large field of view, high duty cycle and increasingly sophisticated detection methods, Fermi GBM is expected to have a major role in the Multi-Messenger era.

        Speaker: Colleen Wilson-Hodge (NASA/MSFC)
      • 12:15 PM
        An Overview of the GBM Targeted Search For Sub-threshold Emission Associated with LIGO/Virgo Detections 15m

        The Fermi Gamma-ray Space Telescope’s Gamma-ray Burst Monitor (GBM) is currently the most prolific detector of Gamma-ray Bursts (GRBs), including short-duration GRBs (sGRBs). Recently the detection rate of sGRBs has been increased dramatically through the use of ground-based searches to analyze untriggered GBM continuous time tagged event (CTTE) data. Motivated by the possibility that sGRBs are caused by compact binary mergers that also produce gravitational waves, the GBM team has developed a method to search CTTE data for transient events in temporal coincidence with a LIGO/Virgo compact binary coalescence trigger. This targeted search operates by looking for a coherent signal in all 14 GBM detectors over a variety of timescales by using spectral templates which are convolved with the GBM detector responses. I will review recent improvements to the targeted search pipeline and discuss its enhanced capabilities at detecting sub-threshold transient signals associated with LIGO/Virgo triggers. I will also discuss the role of the targeted search in finding a possible GBM counterpart to GW150914 and will compare that signal to other known astrophysical transients that can be recovered from the untriggered GBM data using this method.

        Speaker: Daniel Kocevski (NASA/MSFC)
    • 12:30 PM 1:30 PM
      Catered Lunch 1h
    • 1:30 PM 6:30 PM
      Free Afternoon - Social Program
    • 6:30 PM 9:30 PM
      Conference Dinner: Bayernhalle
    • 8:30 AM 10:30 AM
      Galactic Diffuse & CR propagation: Galactic Diffuse Emission
      Convener: Isabelle Grenier
      • 8:30 AM
        Cosmic rays and the diffuse gamma-ray emission 30m

        We discuss the impact that the charged cosmic rays have on the determination of the gamma-ray diffuse galactic emission. We review the implications deriving from present data and outline some future prospects for data and models.

        Speaker: Fiorenza Donato (Torino University)
      • 9:00 AM
        Development of the Galactic Diffuse Emission Model for the LAT 4FGL Catalog Analysis 15m

        In support of analysis for the Large Area Telescope 4FGL source catalog (see invited contribution by Jean Ballet) we are developing a new model for the Galactic diffuse emission, fit to the same 8-year Pass 8 data set, spanning 50 MeV--1 TeV. Relative to the 4-year Pass 7 model developed for the 3FGL catalog, the new model includes updated distributions of interstellar atomic and molecular hydrogen, including gas not traced by spectral line surveys, and more degrees of freedom in the fitting. We are testing new templates, including for unresolved Galactic sources, and as for the 4-year model iteratively including un-modeled extended residuals, e.g., the Fermi bubbles. The goal is for the 8-year model to have reduced systematic uncertainties. In fitting the observations we also include updated models for the emission of the Moon and quiet Sun, spectral models for the isotropic extragalactic emission, and take into account the anisotropic distribution of residual charged particles that are more prominent with the larger instrumental acceptance of Pass 8. We also consider a preliminary 4FGL source list. We will present details of the new model components and its comparison to the data.

        Speaker: Seth Digel (KIPAC/SLAC)
      • 9:15 AM
        Cosmic rays, gas, and dust in local clouds 15m

        The recent progress in HI, CO, dust, and gamma-ray observations provides excellent opportunities to probe the properties of the interstellar medium (ISM) at a resolution of a few parsecs inside nearby clouds and to search for biases in the different gas tracers.

        The nearby clouds in Galactic anti-center and Chamaleon regions have been studied using jointly the gamma-ray observations of Fermi Large Area Telescope, and the dust optical depth inferred from Planck and IRAS observations.

        We have quantified the potential variations in cosmic-ray density and dust properties per gas nucleon across the different gas phases and different clouds, and we have measured the CO-to-H2 conversion factor, XCO, in different environments. We also mapped the gas not seen, or poorly traced, by HI, free-free, and 12CO emissions, namely (i) the opaque HI and diffuse H2 present in the Dark Neutral Medium at the atomic-molecular transition, and (ii) the dense H2 to be added where 12CO lines saturate.

        We will present these results and show how the precise modelling of the ISM we have performed helps to improve the modelling of diffuse Galactic gamma-ray emission.

        Speaker: Quentin REMY (CNRS-LUPM)
      • 9:30 AM
        Diffuse X-ray emission from Loop I: Additional evidence of past activity of Galactic Center and relation to Fermi Bubbles 15m

        The Fermi-LAT discovered giant structures that are barely visible in the EGRET era. The most striking feature is the so-called Fermi bubbles, extending above and below the Galactic center. In addition, Fermi-LAT detected diffuse gamma-ray emissions associated with Loop I. The northern-most part of Loop I is the brightest arm, known as the North Polar Spur (NPS), and is even clearly visible in the ROSAT X-ray sky map. In previous works, we reported on the X-ray observations of the NPS and Galactic halo with the Suzaku and Swift satellites. All the results suggest that the NPS is a giant structure in the Galactic Center (GC) and is heated by the expansion of the Fermi Bubbles with a velocity of Vexp ~ 300 km/s; however, the origin of the X-ray and gamma-ray emissions associated with Loop I is completely unknown. To shed new light on the past activity of the GC, we analyzed all the archival X-ray data pointing toward Loop I with the Suzaku satellite. We argue, for the first time, that the soft gamma-ray spectra of Loop I may be due to π0 decay.

        Speaker: Masahiro Akita (Waseda.univ)
      • 9:45 AM
        Spiral Arm Signatures in Fermi-LAT's spectral index map 15m

        Standard cosmic ray (CR) propagation models that assume neither a time-independent source distribution nor a location-independent diffusion cannot give rise to spatially dependent CR (and hence γ-ray) spectral slopes. Yet, recent observations by Fermi-LAT exhibit a hardening of the γ-ray spectrum between the Sagittarius and Carina tangents, and a further hardening at a few degrees above and below the Galactic plane. Here, we study a model in which the distribution of CR sources is concentrated in the galactic spiral arms, and in particular, that these arms are dynamic. The model has been successful in explaining secondary to primary ratios (e.g., B/C, sub-Iron/Iron, positrons) as well as long term variations in the CR flux over geological time scales. We find unique signatures that agree with the Fermi-LAT observations and also provides a physical explanation to the difference between the local CR spectral slope and the CR slope inferred from the average γ-ray spectrum.

        Speaker: Nir Shaviv (Hebrew University of Jerusalem)
      • 10:00 AM
        High-energy Gamma Rays from the Milky Way: 3D Interstellar Emission Models with GALPROP 15m

        High-energy gamma rays of interstellar origin are produced by the
        interaction of cosmic-ray (CR) particles with the diffuse gas and
        radiation fields in the Galaxy. The main features of this emission are
        well understood and are reproduced by existing CR propagation models
        employing a 2D galactocentric cylindrical symmetric geometry. However,
        the high-quality data from instruments like the Fermi Large Area
        Telescope reveal significant deviations from the 2D model predictions on
        few to tens of degree scales, indicating that the details of the
        Galactic spiral structure should be included and thus require 3D spatial
        modelling. In this contribution the high-energy interstellar emissions
        from the Galaxy are calculated using the latest release of the GALPROP
        code for the first time employing full 3D spatial models for the
        CR source, interstellar gas, and interstellar radiation field (ISRF) densities.
        The interstellar emission models that include arms and bulges for the CR
        source and ISRF densities provide plausible physical interpretations for
        features found in the residual maps from high-energy gamma-ray data analysis.
        The 3D models provide a more realistic basis for interpreting the non-thermal interstellar emissions toward the inner Galaxy and about the Galactic centre.

        Speaker: Troy Porter (Stanford University)
      • 10:15 AM
        Constraining the emission of cosmic electrons from supernova remnants with flux, dipole anisotropy and radio data 15m

        In this contribution we present an interpretation of the most recent data on cosmic-ray electron and positron (CRE) fluxes (from Fermi-LAT, HESS, CALET and AMS-02), with a special focus on the electron contribution from supernova remnants (SNRs). For the first time, we consider together the constraints coming from CRE flux up to 20 TeV, as well as Fermi-LAT dipole upper limits and radio measurements of individual nearby SNRs. We show how CRE data up to 20 TeV can constrain the energy cutoff of the electron emission from a smooth distribution of SNRs in the Galaxy. Also, we explore the consequences of the recent Fermi-LAT measurement of the dipole anisotropy, studying in particular the total emission energy in electrons and spectral index of Vela YZ and the Cygnus Loop SNRs. Finally, we make use of the full radio spectrum of nearby SNRs to constrain their electron injection spectrum. Our results show how the combination of constraints from different observables shed light on the interpretation of present CRE data.

        Speaker: Silvia Manconi (University of Torino and INFN Torino)
    • 10:30 AM 11:00 AM
      Break 30m
    • 11:00 AM 12:50 PM
      Extragalactic diffuse & EBL
      Convener: Seth Digel (KIPAC/SLAC)
      • 11:00 AM
        Cosmic rays, particle acceleration, and Fermi constraints on star and galaxy formation 30m

        Understanding the physics of galaxy formation is an outstanding problem in modern astrophysics. Recent cosmological simulations have demonstrated that feedback by star formation, supernovae and active galactic nuclei appears to be critical in obtaining realistic disk galaxies and to slow down star formation to the small observed rates. However the particular physical processes underlying these feedback processes still remain elusive. In particular, these simulations neglected magnetic fields and relativistic particle populations (so-called cosmic rays). Those are known to provide a pressure support comparable to the thermal gas in our Galaxy and couple dynamically and thermally to the gas, which seriously questions their neglect. After introducing the underlying physical concepts, I will present our recent efforts to model cosmic ray physics in galaxy formation. I will demonstrate that cosmic rays play a decisive role on all scales relevant for the formation of galaxies, from individual supernova remnants up to scales relevant for entire galaxies. Finally, I will discuss the non-thermal radio and gamma-ray emission of Milky-Way like galaxies and how the Fermi space telescope can be used to infer properties relevant for galaxy formation.

        Speaker: Christoph Pfrommer (Leibniz Institut für Astrophysik Potsdam (AIP))
      • 11:30 AM
        Radio and Gamma-Ray Constraints on the Wind, Magnetic Field, and Cosmic Rays along the minor axis of the starburst M82 15m

        Cosmic rays can be probed by their non-thermal emission in the radio and in gamma-ray bands. One-zone models of cosmic rays have been used to match the integrated emission of starburst galaxies. We construct multi-dimensional models of the local starburst M82 using cosmic ray propagation code GALPROP. Using the integrated gamma-ray and radio spectra, along with the vertical distribution of radio emission along the minor axis, we constrain the gas density, magnetic field strength, and cosmic ray population. We show that the wind velocity and diffusion coefficient can be constrained by the morphology of the radio halo. We discuss the interplay between gas density, magnetic field, and outflow velocity and how they effect the emission. We comment on the energetics of cosmic ray species in the system. We provide direct constraints on the dynamical importance of cosmic rays in driving the outflow of the galaxy.

        Speaker: Benjamin Buckman (The Ohio State University)
      • 11:45 AM
        X-ray to gamma-ray virial shock signal from the Coma cluster 15m

        Following evidence for an east-west elongated virial ring around the Coma galaxy cluster in ~220GeV VERITAS data, we search for corresponding signatures in >GeV $\gamma$-rays from Fermi-LAT, and in soft, ~0.1keV X-rays from ROSAT.
        For the ring elongation and orientation inferred from VERITAS, we find a 3.4$\sigma$ LAT excess, and a >5$\sigma$ modelled signature in the ROSAT R1+R2 bands; both signals are maximized at approximately the expected ring parameters.
        The intensities of the ROSAT, Fermi, and VERITAS signals are consistent with the virial shock depositing ~0.3%
        of its energy over a Hubbble time in a nearly flat, p=-dN/dE~2.2 spectrum of relativistic electrons.
        The steep angular profiles of the LAT and ROSAT signals suggest preferential accretion in the plane of the sky, as indicated by the distribution of neighboring large-scale structure.
        The X-ray signal gauges the compression of cosmic-ray electrons as they are advected deeper into the cluster.

        Speaker: Uri Keshet (Ben-Gurion University of the Negev)
      • 12:00 PM
        The Extragalactic Background Light in the Fermi Era 15m

        The extragalactic background light (EBL), from ultra-violet to infrared, that encodes the emission from all stars, galaxies and actively accreting black holes in the observable Universe is critically important to probe models of star formation and galaxy evolution, but remains at present poorly constrained. The Large Area Telescope (LAT), on board Fermi, produced an unprecedented measurement (relying on 750 blazars and the first 9 years of Pass 8 data) of the EBL optical depth at 12 different epochs from redshift 0 up to a redshift of 3. In this talk, we will present the measurement and how it constrains the EBL energy density and its evolution with cosmic time. We will also discuss how this paves the road to the first point-source-independent determinations of the star-formation history of the Universe.

        Speaker: Marco Ajello (Clemson University)
      • 12:15 PM
        Measuring the Cosmic Star Formation Rate Density with Fermi-LAT 15m

        The extragalactic background light (EBL) in the ultraviolet through optical absorbs gamma rays detectable by Fermi-LAT. We used the absorbed gamma-ray spectra of blazars to make the newest measurements of the EBL absorption optical depth. We fit these measurements with an EBL model that allows the cosmic star formation rate density (CSFRD) to vary, thus making the first accurate point-source-independent measurement of the CSFRD; that is, a measurement of the CSFRD using only gamma rays detected by the LAT. This provides strong constraints on the CSFRD at z >~5, with implications for Population III star formation.

        Speaker: Justin Finke (US Naval Research Laboratory)
      • 12:30 PM
        10 yrs AGILE 20m
        Speaker: Marco Tavani
    • 12:50 PM 2:00 PM
      Catered Lunch 1h 10m
    • 2:00 PM 4:00 PM
      Active Galactic Nuclei: III GaPa/2-1 - Konzertsaal (Garmisch-Partenkirchen)

      GaPa/2-1 - Konzertsaal


      Convener: Prof. Eduardo Ros (MPI für Radioastronomie & Universitat de València)
      • 2:00 PM
        The remarkable gamma-ray flaring activity of CTA 102 as seen by the Fermi-LAT 15m

        In late 2016, the Fermi Large Area Telescope (LAT) observed a dramatic increase in the gamma-ray activity from
        the blazar CTA 102. The enhanced state was monitored throughout the whole electromagnetic spectrum and persisted for several weeks, reaching daily gamma-ray fluxes (0.1-100 GeV) as high as 10^-5 ph cm^-2 s^-1. We present the analysis of these flares and discuss their characteristics in the context of extreme blazar flares previously observed by the LAT.

        Speaker: Sara Buson (NASA-GSFC)
      • 2:15 PM
        Detection of intra-day variability in FSRQ CTA 102 during high state 15m

        The flux variability of blazars can shed light on the innermost region of jets well beyond the imaging capabilities of present generation telescopes in any part of the electromagnetic spectrum. The FSRQ, CTA 102 (z ~ 1) started showing activity in gamma-rays during 2016 with a few very bright flares. The detection of intra-day variability above 100 MeV using Fermi-LAT during these flares allows to constrain the gamma-ray emission region in CTA 102. The inferred compactness of the emission region suggests, an origin of the gamma-rays close to the central engine and a low pair-creation opacity of the broad-line emission region, or a hadronic emission scenario outside of BLR region.

        Speaker: Amit Shukla (University of Würzburg)
      • 2:30 PM
        Unravelling the complex behaviour of our closest very-high-energy gamma-ray blazars, Mrk421 and Mrk501 15m

        Because of their brightness and proximity (z=0.03), Mrk421 and Mrk501 are among the very-high-energy (>100 GeV) gamma-ray objects that can be studied with the greatest level of detail, and consequently they are excellent astrophysical high-energy physics laboratories to study the nature of blazars. Motivated by the extensive temporal exposure of Fermi-LAT, since 2008, there has been an unprecedentedly long and dense monitoring of the radio to very-high-energy gamma-ray emission from these two archetypical TeV blazars. In this conference, I will report some highlight results obtained from these multiwavelength campaigns. Despite some differences in the variability patterns of these two sources, there are also a number of similarities that support a broadband emission dominated by leptonic scenarios, as well as indications for in situ electron acceleration in multiple compact regions. I will also show the presence of different flavors of flaring activity and discuss the complexity in the temporal evolution of their broadband emission, which demonstrates the importance of performing a continuous monitoring over multi-year timescales to fully characterise the dynamics of blazars.

        Speaker: David Paneque (Max Planck Institute for Physics)
      • 2:45 PM
        The FSRQ PKS 1510-089: The Gamma-ray–Synchrotron Connection 15m

        The flat spectrum radio quasar (FSRQ) PKS 1510-089 (z=0.361) is known for its complex multi-wavelength behaviour. Since 2015, it has been very active across the entire electromagnetic spectrum. This has lead to joint observation campaigns including Fermi-LAT, Cherenkov telescopes and several instrument covering the synchrotron branch. Observations resulted in a range of remarkable measurements, including rapid flares above 200 GeV – peaking at more than 30 times long-term average – and unprecedented optical flares peaking in R-band at 13.6 magnitudes – almost 6 times long-term average. The comparison of the different instrument's results also show that different events follow different spectral evolution within the gamma-ray band and display different relationships to the synchrotron emission. We discuss the effect of pair-absorption on flares originating at different distances from the core and conclude that absorption in the BLR is not the sole reason for the broad-band diversity.

        Speaker: Felix Jankowsky (LSW Heidelberg)
      • 3:00 PM
        Orphan $\gamma$-ray Flares and Stationary Sheaths of Blazar Jets 15m

        Many $\gamma$-ray flares within blazars are highly correlated with flares detected at longer wavelengths; however, a small subset appears to occur in isolation. These orphan $\gamma$-ray flares challenge models of blazar variability. We have developed the 'Ring of Fire' model to explain the origin of these orphan flares. In this model, electrons contained within a blob of plasma moving relativistically along the jet spine inverse-Compton scatter synchrotron photons emanating off of a ring of shocked sheath plasma that enshrouds the jet spine. As the blob propagates through the ring, the scattering of the ring photons by the blob electrons creates an orphan $\gamma$-ray flare. This model has been successfully applied to modeling an orphan $\gamma$-ray flare in the blazar PKS 1510$-$089. To further support the plausibility of this model, we have created a stacked radio map of PKS 1510$-$089 that exhibits a prominent polarimetric signature of a sheath of plasma surrounding the spine of the jet. We have since extended our modeling and stacking techniques to a larger sample of blazars: 3C 273, 4C 71$.$01, 3C 279, 1055$+$018, CTA 102, and 3C 345, most of which exhibit orphan $\gamma$-ray flares.

        Speaker: Dr Nicholas MacDonald (MPIfR)
      • 3:15 PM
        Long-Term Study of the Light Curve of PKS 1510-089 in GeV energies 15m

        We have analyzed data from the flat-spectrum radio quasars PKS 1510-089 collected over a period of eight years from 2008 August to 2016 December with the Fermi-LAT. We have identified several flares of this highly variable source, studied their temporal and spectral properties in detail, and compared with previous works on flares of PKS 1510-089. Five major flares and few sub-flares have been identified in our study. The fastest variability time is found to be 1.30$\pm$0.18 hr and the minimum size of the emission region is found to be 4.85$\times$10$^{15}$ cm. In most of the flares, the spectral energy distribution are better fitted with a log-parabolic distribution compared to a simple power law or a power law with exponential cutoffs. This has strong physics implications regarding the nature of the high-energy gamma-ray emission region.

        Speaker: RAJ PRINCE (Raman Research Institute, Bangalore, INDIA)
      • 3:30 PM
        Blazar Radio and Optical Survey (BROS): A New Catalog of Blazar Candidates 15m

        By using deep radio source catalogs currently available, we present a new blazar candidate catalog, BROS, which includes 56314 sources located at declination δ>−40∘ and outside the Galactic Plane (|b|>10). We picked up flat-spectrum radio sources of α>−0.5 (α is defined as Fν∝ν^α) from 0.15 GHz TGSS and 1.4 GHz NVSS catalogs. Then, we identified their optical counterparts by cross-matching with the Pan-STARRS1 data. Color-color and color-magnitude plots for the selected flat-spectrum radio sources clearly showed two populations, “quasar-like” and “elliptical-galaxy-like” sequences. We emphasize that the latter population emerged for the first time and is missed by previous CRATES catalog because of the higher radio flux threshold. This BROS catalog is useful to search for counterparts of Fermi extragalactic un-ID objects as well as PeV neutrions detected by IceCube. We also emphasize that this BROS catalog includes nearby (z≤0.3) BL Lac objects, a fraction of which would be TeV emitters and detectable by future Cherenkov Telescope Array. We will soon make this catalog available once published.

        Speaker: Dr Yasuyuki Tanaka (Hiroshima)
      • 3:45 PM

        We present an analysis of 8 years of Fermi-LAT γ-ray data obtained for NGC 1275. By examining the changes in its flux and spectral shape over the entire dataset, we found that its spectral behavior changed around 2011 February. The γ-ray spectra at the early times evolves largely at high energies, while the photon indices were unchanged in the latter despite rather large flux variations. To explain these observations, we suggest the flux changes in the early times were caused by injection of high-energy electrons into the jet, while later, the γ-ray flares were caused by a changing Doppler factor. To demonstrate the viability of these scenarios, we fit the broad-band spectral energy distribution data with a one-zone synchrotron self-Compton (SSC) model for flaring and quiescent intervals before and after 2011 February. To explain the γ-ray spectral behavior, the maximum electron Lorentz factor would have changed from γmax = 2.5 × 10^5 (quiescence) to γmax = 3.5 × 10^5 (flare) in the early times, while a modest change in the Doppler factor from δ = 2.7 to δ = 3.6 adequately fits the quiescent and flaring state γ-ray spectra in the later times.

        Speaker: Kazuhisa Tanada (Waseda University)
    • 2:00 PM 4:00 PM
      Extragalactic diffuse & EBL II GaPa/1-1 - Olympiasaal (Garmisch-Partenkirchen)

      GaPa/1-1 - Olympiasaal


      Convener: Seth Digel (KIPAC/SLAC)
      • 2:00 PM
        Exploring the full information content of the extragalactic gamma-ray sky maps 30m

        The main tools typically used to investigate the nature of the extragalactic gamma-ray background (EGB) are its energy spectrum and population studies of resolved point sources.
        However, a larger amount of information is contained in the full gamma-ray maps, and this can be exploited to further push the study of the EGB.
        This information can be encoded into different observables like the auto-correlation, the pixel statistics and the cross-correlation.
        In the talk I will review these complementary observables, the current status, measurements, and the constraints on the EGB derived from them, with
        some emphasis on the cross-correlation with galaxy catalogs.

        Speaker: Alessandro Cuoco (RWTH Aachen TTK)
      • 2:30 PM
        Measuring the Galaxy Luminosity Density out to z~6 with Fermi-LAT 15m

        The Extragalactic Background Light (EBL) absorbs gamma-rays (γγ->e-e+) and leaves a characteristic imprint in the spectra of high energy blazars. Utilizing the new Fermi-LAT measurement of the gamma-ray optical depth at 0<z<3, we reconstruct the detailed build-up of the EBL over cosmic time in a model-independent way. We use an MCMC approach to determine the instantaneous luminosity density of galaxy populations from the UV to the near-IR out to z~6. This allows us to constrain both the cosmic star formation rate density and the build-up of stellar mass over 90% of cosmic time. We also present limits on the amount light from faint undetected galaxies during the epoch of reionization.

        Speaker: Kari Helgason (Max Planck Institute for Astrophysics)
      • 2:45 PM
        The Density of Blazars above 100 MeV and the Origin of the Extragalactic Gamma-ray Background 15m

        Relying on the first 104 months of Fermi-LAT Pass 8 data, using detailed Monte Carlo simulations, we obtained the most sensitive measurement of the source count distribution of blazars above 100 MeV. The result shows, with high statistical significance, the presence of a break in the distribution at low fluxes. From this, we provide a precise measurement of the contribution of blazars to the extragalactic gamma-ray background (EGB). Furthermore, we confirm that they can not account for the total EGB, therefore, another source class is required to explain the remaining component. In this talk, we will present this new measurement and discuss alternatives for the origin of the missing EGB component.

        Speaker: lea marcotulli (clemson university)
      • 3:00 PM
        Extragalactic Background Light Measurements from a Combined Likelihood Analysis of Blazars Detected with the MAGIC Telescopes 15m

        Recent results on the Extragalactic Background Light (EBL) intensity obtained from a combined likelihood analysis of blazar spectra detected by the MAGIC telescopes are reported. The EBL is the optical-infrared diffuse background light accumulated during galaxy evolution, directly and/or reprocessed by dust, which provides unique information about the history of galaxy formation. The low energy photons from the EBL may interact with very high energy (VHE, E > 100 GeV) photons from blazars. This interaction between the EBL and the gamma-ray photons leaves an energy-dependent imprint of the EBL on the VHE gamma-ray spectra of the blazars. Therefore, the study of their spectra can be used to constrain the EBL density at different wavelengths and its evolution in time. In the last few years the MAGIC telescopes obtained accurate measurements of the spectra of 12 blazars in the redshift range from z=0.03 to z=0.944 for over 300 hours of observation. This allows us to extend the redshift coverage and improve upon previous constraints on EBL, which turn out to be compatible with state-of-the-art models. We conclude that these new measurements are limited by systematic uncertainties.

        Speaker: Alberto Dominguez (Universidad Complutense de Madrid)
      • 3:15 PM
        Study of the anisotropy of the unresolved gamma-ray background 15m

        The Extragalactic gamma-ray Emission (EGB) is constituted by two essential parts: resolved gamma-ray sources, point-like or extended, and an isotropic component. Once the formers have been excluded (masked or subtracted), what remains is the latter component, called Unresolved Gamma-Ray Background (UGRB), which, at a deeper level, is not truly isotropic and includes contribution from unresolved populations of sources. Expanding the UGRB sky map into spherical harmonics gives a powerful mean to study the intensity fluctuations even at the smallest scales, which can give clues about what this component is made of.
        In this analysis we study the UGRB anisotropy signal with 8 years of Fermi-LAT Pass 8 data. An energy-dependent mask has been built to cover each resolved source in addiction to a region around the Galactic plane. Preliminary results are compatible with at least two classes of point-like sources contributing the UGRB emission.

        Speaker: Michela Negro
      • 3:30 PM
        Updated Fermi-LAT Constraints on the Extragalactic Background Light 15m

        The extragalactic background light (EBL) is a fundamental cosmological observable of our universe, allowing insight into the history of star formation within our universe. Extending between 0.1 - 1000 $\mu$m, it is the UV to near-IR that is of interest in high and very high energy astronomy, where EBL photons interact via pair production to leave a visible imprint in the spectra of distant AGN. Multiple studies have been carried out using ground-based Cherenkov telescopes, which can observe the spectra of relatively nearby AGN to provide limits on the density of the EBL. These however do not reveal a great amount of detail concerning the evolution of the EBL with time, and therefore the star formation rate. The Fermi-LAT instrument, with its long exposure of the extragalactic sky, holds an extensive sample of AGN extending out to large redshifts (z < 2.56) and has been used by the Fermi-LAT collaboration to study the EBL. Here we further that study by combining a sample of 259 AGN, carefully modelling their spectral energy distributions and determine a redshift-dependent EBL correction factors to a range of models, taking into account the temporal and spectral variability of sources.

        Speaker: Thomas Armstrong (University of Oxford)
      • 3:45 PM
        Deriving the contribution of point sources to the Extragalactic gamma-ray background with efficiency corrections and photon statistics 15m

        The Fermi-LAT has confirmed and measured with unprecedent precision the extragalactic gamma-ray background (EGB), which is the sum of the flux of cataloged sources and the Isotropic diffuse gamma-ray background (IGRB). The IGRB is a highly-isotropic component on angular scales larger than 1 degree and whose composition is thought to be dominated by unresolved sources, i.e., sources that are not individually detected by the LAT.
        We investigate the origin of the EGB using for the first time two complementary techniques: 1) a source-detection efficiency correction method and 2) an analysis of pixel photon count statistics with the 1-point probability distribution function (1pPDF). With the first method, using realistic Monte Carlo simulations of the gamma-ray sky, we calculate the efficiency of the LAT to detect point sources and this enables us to find the intrinsic source count distribution at photon fluxes. The source count distribution derived with this method is then compared to the one found with the 1pPDF method. The results obtained with these two methods are independent from extrapolation of fluxes below the sensitivity of the LAT and provide a precise estimation of the contribution of blazars to the Fermi EGB.

        Speaker: MATTIA DI MAURO (Stanford University)
    • 4:00 PM 4:30 PM
      Coffee Break 30m
    • 4:30 PM 6:00 PM
      Analysis techniques II: Catalogs GaPa/1-1 - Olympiasaal (Garmisch-Partenkirchen)

      GaPa/1-1 - Olympiasaal


      Convener: David Paneque (Max Planck Institute for Physics)
      • 4:30 PM
        Improving the Fermi LAT source catalog and interstellar emission model 30m

        The current Fermi-LAT source catalog (3FGL: 3033 sources above 100 MeV) and interstellar emission model were based on four years of Pass 7 data. The more recent 3FHL catalog was restricted to energies larger than 10 GeV. The next full LAT source catalog (4FGL) will be based on 8 years of Pass 8 data. With this much larger statistics, below a few GeV the source detection and characterization is increasingly limited by imperfect knowledge of the interstellar emission, which dominates the gamma-ray sky. This effect is particularly strong near the Galactic plane, but is important up to a few 100 MeV over the entire sky.
        On one side, we are working to improve the interstellar emission model. Besides the more precise LAT data, this benefits from external input, particularly recent all-sky HI surveys and the Planck dust map. On the other side, we are down-weighting pixels with many counts in the maximum likelihood fitting in order to account (approximately) for systematics in the source detection statistic and in the parameter uncertainties. I will describe those efforts and present an early version of the 4FGL catalog. More specialized catalogs (AGN, pulsars) will follow.

        Speaker: Jean Ballet (DAp/AIM, CEA Saclay)
      • 5:00 PM
        The second catalog of flaring gamma-ray sources (2FAV): observing astrophysical accelerators in real time 15m

        Particle acceleration to relativistic energies is common in the Universe. A wealth of astrophysical accelerators have been identified over the past decades using gamma-ray observations. Particularly interesting are time variable sources, where the acceleration and radiation processes can be observed over time. Recently, the LAT collaboration has published a second catalog of flaring gamma-ray sources (2FAV). The catalog is based on 7.4 years of observations, during which 518 flaring sources where detected on weekly time scales. Out of these, 77 had not been seen in gamma-rays before. In addition, the catalog pipeline is used to analyse LAT data in real time. The results are made public on an interactive web page. In this presentation, I will review the different classes of variable gamma-ray sources based on the 2FAV and give an outlook on future developments.

        Speaker: Rolf Buehler (DESY)
      • 5:15 PM
        Effects of Biases of the Interstellar Emission Models on Point Source Finding and Characterization with the Fermi-LAT 15m

        In this contribution we present studies to quantify the effects of possible biases in diffuse emission models for LAT data on point-source finding and spectral parameter extraction. In particular, 1) we examine differences in source lists obtained in a 40 degree by 40 degree region around the Galactic center (GC region) using different interstellar emission models (IEMs), 2) examine the goodness-of-fit of models of the GC region that include the IEMs as well as discrete sources, 3) use a likelihood weighting scheme to include systematic uncertainties of the IEMs in the point-source fitting. We find that almost all of the differences away from the Galactic plane (|b| > 5 degrees) are attributable to the effect of the source-detection threshold in combination with small differences in the IEMs. On the other hand, along the Galactic plane, we find that biases in the IEMs can result in clusters of spurious sources in regions where the IEMs significantly under-predict the data as well as in groups of missed sources in regions where the IEMs over-predict the data. However, we find that these effects are well mitigated by the likelihood weighting scheme.

        Speaker: Eric Charles (SLAC)
      • 5:30 PM
        The First Catalog of Low Energy Fermi-LAT sources 15m

        Previous analyses of point sources in the gamma-ray range were done only below 30 MeV (COMPTEL) or above 100 MeV (Fermi-Large Area Telescope, EGRET). Below 30 MeV, the imaging Compton telescope (COMPTEL) onboard NASA's Compton Gamma-Ray Observatory detected 26 steady sources in the energy range from 0.70 to 30 MeV. At high energy, the LAT, on board the Fermi satellite, detects more than three thousands sources between 100 MeV and 300 GeV (3FGL). Since the Fermi-LAT detects gamma rays down to 20 MeV, we create a list of sources detected in the energy range between 30 MeV and 100 MeV, using PGWave, a background independent tool that makes use of a wavelet-based method. This closes a gap of point source analysis between the COMPTEL catalog and the Fermi-LAT and EGRET catalogs. We present the Fermi-LAT low energy catalog (1FLE) of sources detected in the 30 MeV - 100 MeV range, based on 8 years and 9 months of Fermi-LAT data.

        Speaker: Giacomo Principe (ECAP, Erlangen Nuernberg University)
      • 5:45 PM
        Calorimeter-less gamma-ray telescopes: Optimal measurement of charged particle momentum from multiple scattering by Bayesian analysis of filtering innovations. 15m

        Novel gamma-ray telescope schemes are under development so as to bridge the 0.1-100 MeV sensitivity gap of gamma-ray astronomy (Compton, pair creation), (silicon wafer stacks, emulsions, gas detectors).
        The lower average density with respect, e.g. to the tungsten/silicon active target of the Fermi-LAT makes square-meter effective area telescopes voluminous objects, for which the photon energy measurement by conventional means (calorimeter, magnetic spectrometer, transition radiation detector) is a challenge for the mass budget.

        We present an optimal measurement of track momentum by the multiple measurement of the angular deflections induced by multiple scattering in the active target itself, using a Bayesian analysis of the filtering innovations of a series of Kalman filters applied to the track.

        For a Silicon-wafer-stack telescope, the method yields meaningful results up to a couple of GeV/c. (Eq. (58) and Fig. 10 of Nuclear Inst. and Methods in Physics Research, A 867 (2017) 182, arXiv:1706.05863 )

        Speaker: Denis Bernard (LLR, Ecole Polytechnique & CNRS/IN2P3)
    • 4:30 PM 6:00 PM
      Dark Matter GaPa/2-1 - Konzertsaal (Garmisch-Partenkirchen)

      GaPa/2-1 - Konzertsaal


      Convener: Alessandro Cuoco (RWTH Aachen TTK)
      • 4:30 PM
        Indirect Axion and Axionlike Particle Searches at Gamma-Ray Energies 30m

        Axions and axionlike particles (ALPs) are dark-matter candidates that occur in a variety of extensions of the Standard Model. They couple to photons in the presence of electromangetic fields, making them potentially detectable. Due to the ubiquitous presence of magnetic fields in the Universe, astrophysical sources are particularly well suited to search for traces of these particles.

        I will give an overview over axion and ALP searches at gamma-ray energies. In particular, I will present constraints on the photon-ALP coupling derived from Fermi Large Area Telescope observations of the NGC 1275, the central galaxy of the Perseus cluster. The bounds are the strongest to date in the ALP mass range between 0.5 and 20 neV and surpass the sensitivity of future dedicated laboratory experiments. Further, I will give an outlook on future ALP searches using core-collapse supernovae and future gamma-ray instruments such as the Cherenkov Telescope Array and satellite missions.

        Speaker: Manuel Meyer
      • 5:00 PM
        Dark matter theory: implications and future prospects for Fermi 30m

        I will review the implications of Fermi data for theories of the identity of dark matter, and their combination with data from other complementary probes. I will also preview some of the prospects for probing such models with future data.

        Speaker: Pat Scott (Imperial College London)
      • 5:30 PM
        Probing the nature of dark matter with gamma rays: what we learned from the LAT and prospects for the CTA 15m

        High-energy gamma rays are one of the most promising tools to constrain or reveal the nature of dark matter, in particular the Weakly Interacting Massive Particles (WIMP) models. The Cherenkov Telescope Array (CTA) is well into its pre-construction phase and will soon probe the high energy gamma ray sky in the ~50 GeV - 100 TeV energy range, probing a parameter space of heavier dark matter (above ~100 GeV), with unprecedented sensitivity.

        One of the main targets for searches for signals of dark matter annihilation or decay is the centre of our Galaxy. Due to the its lower energy threshold and significantly larger effective area when compared to the current generation of ground based Cherenkov telescopes, the CTA is expected to be sensitive to diffuse astrophysical emission also present in that region. In this talk we report the status of the collaboration effort to, based on the astrophysical emission observed with the LAT at lower energies, study the impact of extended astrophysical emission backgrounds on dark matter search and to suggest the promising data analysis and observational strategies for the upcoming CTA data.

        Speaker: Gabrijela Zaharijas (University of Nova Gorica)
      • 5:45 PM
        Limits on Dark Matter annihilation signal from dwarf galaxies with prior-free astrophysical factors 15m

        Dwarf spheroidal galaxies (dSphs) are considered promising targets for indirect Dark Matter (DM) identification. The (mostly frequentist) analyses of gamma-ray photons originating from dSphs have allowed to set stringent limits on the DM self-annihilation cross-section. Conventional search strategies rely on quantifying the abundance of DM, by calculating the so-called J-factor. This quantity can be estimated from the kinematic properties of the stellar population of dSphs by means of Bayesian methods, which introduce significant systematic uncertainties due to the inevitable influence of priors. Here we describe a fully frequentist method for deriving J-factors and their uncertainties, which improves upon previous studies by making the statistical treatment of J more consistent with most gamma-ray analyses. Validation is performed using the simulation suite released by Gaia Challenge, showing that the method possesses good statistical properties. We apply the technique on a kinematic sample from 20 dSphs. We also implement our likelihoods of J to derive new upper limits on the DM annihilation cross-section. The new limits and the implications of these findings for DM searches are discussed.

        Speaker: Andrea Chiappo (Oskar Klein Centre, Stockholm University)
    • 8:30 AM 10:30 AM
      Neutrino-Gamma connection & The Sun
      Convener: Elena Orlando (Stanford University)
      • 8:30 AM
        Fermi Large Area Telescope observations of the Sun: The first ten years 30m

        The Fermi Large Area Telescope (LAT) observations of the active Sun provide the largest sample of detected solar flares with emission greater than 30 MeV to date. These include detections of impulsive and sustained emission, extending up to ~20 hours in the case of the 2012 March 7 X-class flares. Of particular interest is the first detection of >100 MeV gamma-ray emission from three solar flares whose positions behind the limb were confirmed by the STEREO spacecrafts. The LAT data provides a new observational channel that, when combined with observations from across the electromagnetic spectrum, provide a unique opportunity to diagnose the mechanisms of high-energy emission and particle acceleration in solar flares. We will present an overview of these observations including the emission of the Sun in its quiescent state and discuss how these observations provide constrains on different emission mechanisms.

        Speaker: Melissa Pesce-Rollins (INFN-Pisa)
      • 9:00 AM
        Search for GeV neutrinos associated with solar flares with IceCube 15m

        Solar flare neutrinos from the decay of mesons produced in collisions of accelerated ions from the solar atmosphere are expected with energies of O(MeV-Gev). The study of such neutrinos, combined with existing gamma-ray observations by Fermi-LAT, would provide a novel window to the underlying physics of the acceleration process. The IceCube Neutrino Observatory may be sensitive to solar flare neutrinos and therefore provides a possibility to measure the signal or establish more stringent upper limits on the solar flare neutrino flux. Results from a new approach to search dedicated to low energy neutrinos coming from transient events will be presented. It combines a time profile analysis and an optimized selection of solar flare events based on Fermi-LAT observations, significantly lowering the energy threshold of IceCube, which was initially designed to detect neutrinos with energies above O(100 GeV) and above.

        Speaker: Gwenhaël de Wasseige
      • 9:15 AM
        Origin of cosmic neutrinos in the Fermi context 30m

        I discuss the results of IceCube's astrophysical neutrino observations in the context of Fermi data. Examples are constraints on the contribution to the observed diffuse neutrino flux from AGNs and GRBs from stacking analyses using catalogues, and generic conclusions about the neutrino production mechanism from Fermi's extragalactic diffuse flux measurements. I will also point out theoretical implications and future prospects.

        Speaker: Walter Winter (DESY)
      • 9:45 AM
        A minimal model for extragalactic cosmic rays and neutrinos 15m

        I discuss attempts to explain in a unified way the experimental data on ultrahigh energy neutrinos and cosmic rays, using a single source class and obeying data on cosmic ray composition and limits on the extragalactic diffuse gamma-ray background.

        Speaker: Michael Kachelriess (NTNU)
      • 10:15 AM
        On the Detection Potential of Short Blazar Flares for Current Neutrino Telescopes 15m

        High-confidence associations of individual neutrinos with individual blazars could be achieved via spatially and temporally coincident detections of photons and high-energy neutrinos (>100 TeV) from short blazar flares. It has been suggested that the current IceCube neutrino detector is sufficiently sensitive to detect neutrinos from such short flares.
        We want to test this prediction by calculating the expected number of neutrinos produced in the IceCube detector for the 50 brightest short blazar flares in the sky.
        The two blazars 3C 279 and PKS 1510−089 alone account for the 27 highest-ranked flares, while the 50 best-ranked flares are produced by a group of only seven different sources.
        We find that the fluence of most individual blazar flares is far too small to yield a substantial Poisson probability for the detection of one or more neutrinos with IceCube.
        The integrated fluence of the 50 highest-ranked flares yields only about 50 % of Poisson probability for the detection of a single high-energy neutrino. For the most spectacular short blazar flares, however, Poisson probabilities of up to ∼ 2 % are calculated, so that the possibility of associated neutrino detections in future data unblindings of IceCube and KM3NeT seems reasonable.

        Speaker: Mr Michael Kreter (University of Wuerzburg)
    • 10:30 AM 11:00 AM
      Break 30m
    • 11:00 AM 12:15 PM
      Future gamma-ray satellite missions
      Convener: Marco Ajello (Clemson University)
      • 11:00 AM
        The Path from COSI to COSI-X 15m

        COSI, the Compton Spectrometer and Imager, is a balloon-borne gamma-ray telescope (0.2-5 MeV) utilizing high-purity Germanium double-sided strip detectors. In spring 2016, COSI had a very successful 46-day balloon flight from Wanaka, New Zealand, utilizing NASA’s new super-pressure balloon platform, taking COSI 1.5 times around the world. During the flight, COSI observed gamma-ray bursts, compact objects, the Galactic 511-keV annihilation emission, Galactic nucleosynthesis, and relativistic electron precipitation events.
        In summer 2017, an upgraded version of COSI called COSI-X was selected for a Phase A study as a mission of opportunity under NASA’s Explorer program. COSI-X will feature more detectors with higher position resolution, an updated read-out system, and an improved anti-coincidence system, which will all together lead to significantly improved angular resolution, more resolved Compton events, higher effective area, better background rejection, and an overall higher instrument sensitivity. The first of three proposed balloon flights is planned for 2021-2023.
        In the presentation, we will show the latest analysis results from COSI and detail the path forward from COSI to COSI-X.

        Speaker: Andreas Zoglauer (UC Berkeley)
      • 11:15 AM
        Polarimetry and high angular resolution gamma-ray observations in the MeV regime using a novel detector concept 15m

        We have demonstrated, for the first time, that the polarisation of gamma rays in the 1-75 MeV regime can be measured using a novel detection technique, namely tracking the gamma-ray conversion pairs using a gaseous TPC. HARPO (the hermetic argon polarimeter) is, to
        date, the only instrument to have successfully carried out this measurement. Having demonstrated that a TPC can be used to detect and measure the polarisation of MeV gamma rays, we have begun a new, larger study with the goal of flying a TPC on a balloon to validate its preformance in a background-dominated environment. We will describe the mission concept for this gamma-ray polarimeter and also the science that can be addressed both with this demonstrator and with an ultimate, satellite-based instrument.

        Speaker: Deirdre Horan (LLR / Ecole Polytechnique / CNRS / IN2P3)
      • 11:30 AM
        All-Sky Medium Energy Gamma-ray Observatory (AMEGO) - A discovery mission for the MeV gamma-ray band 15m

        The MeV domain is one of the most underexplored windows on the Universe. From astrophysical jets and extreme physics of compact objects to a large population of unidentified objects, fundamental astrophysics questions can be addressed by a mission that opens a window into the MeV range. AMEGO is a wide-field gamma-ray telescope with sensitivity from ~200 keV to >10 GeV. AMEGO provides three new capabilities in MeV astrophysics: sensitive continuum spectral studies, polarization measurements, and nuclear line spectroscopy. AMEGO will consist of four hardware subsystems: a double-sided silicon strip tracker with analog readout, a segmented CZT calorimeter, a segmented CsI calorimeter and a plastic scintillator anticoincidence detector, and will operate primarily in an all-sky survey mode. In this presentation we will describe the AMEGO mission concept and scientific performance.

        Speaker: Jeremy Perkins (NASA/GSFC)
      • 11:45 AM
        Viability of a nano-satellite Compton space telescope 15m

        Since the end of the COMPTEL mission, almost 20 years ago, there haven’t been any new space telescopes able to improve the observations in the electromagnetic energy region above 1 MeV. This energy band, where Compton scattering is the dominating interaction with matter, is of fundamental importance for the understanding of the emission mechanisms in several astrophysical source types.
        Through GEANT 4 simulations, we explore the viability of future observations by means of a nano-satellite Compton telescope. In particular, we aim to achieve COMPTEL's sensitivity level near 1 MeV.
        Low costs and ability to be relatively quickly developed and launched would allow a short-term solution for the lack of new observations in the MeV region, before any large mission takes over.

        Speaker: Francesco Berlato (Max Planck Institute for Extraterrestrial Physics)
      • 12:00 PM
        Monitoring of gamma-ray burst with a fleet of nanosatellites 15m

        With gamma-ray burst (GRB) observations by Swift, Fermi, and HETE-2 and their follow-up observations at other wavelengths, we have made substantial progress in the understanding of their progenitors, physical properties of ultra-relativistic jets, and the emission mechanisms. However, our understanding short GRBs in particular, remains incomplete. New observational probes such as detections of gravitational wave counterparts will provide important new constraints.
        We will present the current status of a feasibility study for a fleet of nano-satellites to perform an all sky monitoring and timing based localisation of GRBs. The fleet of about dozen satellites of the CubeSat standard, equipped with scintillator based soft gamma-ray detectors and GPS receivers for time synchronisation, will measure the time difference between the arrival of the gamma-ray signal at the different satellites. Based on the precise timing and the in-orbit positions of the satellites, the location of the source in the sky will be determined by triangulation. The satellites will downlink data about the detected GRBs within minutes, enabling rapid follow-up observations at other wavelengths and providing an opportunity to detect the electromagnetic counterparts of gravitational waves (GW).

        Speaker: Masanori Ohno (Hiroshima University)
    • 12:15 PM 12:45 PM
      Concluding Remarks
      Convener: Julie McEnery (NASA/GSFC)
      • 12:15 PM
        Remembering Nanni Bignami 15m
        Speaker: Marco Tavani
      • 12:30 PM
        Concluding Remarks 15m
        Speaker: Julie McEnery (NASA/GSFC)