# Mapping the X-ray Sky with SRG: First Results from eROSITA and ART-XC

Europe/Berlin
Garching

#### Garching

Description

IMPORTANT NOTICE

Update March 27, 2020: The reimbursement of all conference fees is now completed. Please let us know if you have not received it within one week from now.

Due to the developing and uncertain situation with the corona virus, and increasing restrictions on travel being placed on many participants, we regret to inform you that we have decided to postpone the SRG2020 conference to a later date. We recommend that you cancel your travel bookings immediately.  We are currently investigating ways to reimburse the conference fees.

Please accept our sincere apologies for any disruption caused.

Further details about the rescheduling of the conference will follow in due course.

Scientific Rationale:

In little more than half a century, X-ray astronomy has established itself as a fundamental domain of observational astrophysics. X-rays probe the hot and energetic components of the Universe, encompassing, among others, the million degree coronae of stars, the remnants of supernovae, the ultra-dense matter in neutron stars, the immediate surroundings of black holes, the plasma filling galaxy clusters – the most massive objects in the Universe.

Successfully launched in July 2019, after more than a decade of development, the Russian-German Spectrum-RG (SRG) mission will contribute to the X-ray exploration of the Universe by performing eight all-sky surveys, each lasting half a year, with its two scientific instruments: eROSITA, the German-built telescope array operating between ~0.3-8 keV, and ART-XC, the Russian-built hard-X-ray focusing telescope array, operating between ~3-30 keV.

As in any other astrophysics domain, the SRG all-sky surveys will unlock large swathes of discovery space, provide large statistical samples to trace the cosmic evolution of various classes of objects, and explore sufficiently large volumes to serve as cosmological tools for the study the Universe as a whole. In particular, the high sensitivity, large field of view, and high survey efficiency of eROSITA is bound to revolutionize X-ray astronomy: within just the first year of operation it will discover about as many new celestial X-ray objects as have been discovered from 1962 until today.

The goal of the next international SRG conference (the third in a series, and the first after the SRG launch) is to discuss the state of the art in the different scientific areas addressed by the mission, present to the community the first results from eROSITA and ART-XC, and explore the synergies with surveys and observations at other wavelengths.

We plan to cover the following topics:

• Galaxy clusters and cosmology
• Physical properties of clusters and groups of galaxies
• Large scale structure of the Universe
• Clusters as cosmological tools
• Active galactic nuclei
• Evolution and properties of the AGN population
• Quasars at high redshift
• AGN as tracers of large scale structure
• Galactic compact objects, stars and planets
• X-ray emission from planets and comets
• X-ray stellar populations of the Milky Way
• Cataclysmic variables and X-ray binaries
• Isolated neutron stars
• ULX and X-ray sources in nearby galaxies
• The Transient X-ray sky
• Tidal Disruption Events
• Gamma-ray bursts and afterglows
• Galactic X-ray transients
• Diffuse X-ray emission
• Cosmic X-ray background and its fluctuations
• Galactic Ridge X-ray Emission
• Hot ISM in the Milky Way, LMC and SMC
• Supernova remnants
• Synergy with multi-wavelength surveys
Participants
• Agata Różańska
• Aishwarya Paliwal
• Akos Bogdan
• Alejandra Fresco
• Alex Markowitz
• Alexander Lutovinov
• Alexander Meshcheryakov
• Alexey Tkachenko
• Alison Coil
• Anatoly Iyudin
• Andrea Botteon
• Andrea Comastri
• Andrea Merloni
• Andreas von Kienlin
• Andrew Strong
• Andrey Semena
• Andrey Shtykovsky
• Angie Veronica
• Ann Hornschemeier
• Anna Ho
• Antara Basu-Zych
• Armin Vahdat Motlagh
• Arne Rau
• Avishay Gal-Yam
• Axel Schwope
• Aysegul Tumer
• Barbara De Marco
• Beate Stelzer
• Beibhinn Whelan
• Ben Maughan
• Bret Lehmer
• Cai Wood
• Chandreyee Maitra
• Chien-Ting Chen
• Chris Tenzer
• Christian Schneider
• Christine Jones
• Daisuke Nagai
• Dan McCammon
• David Alexander
• David Bogensberger
• David Russell
• Didier Kileba
• Diogo Coutinho
• Dominik Bomans
• Doug Swartz
• Duy Hoang
• Ece KILERCI-ESER
• Edward Upsdell
• Efrain Gatuzz
• Ekaterina Filippova
• Enza Magaudda
• Eran Ofek
• Ergun Ege
• Erik Kuulkers
• Erin Kara
• Erwin Lau
• Esra Bulbul
• Eugene Churazov
• Felix Aharonian
• Florian Pacaud
• Francois Mernier
• Frank Haberl
• Gabriele Ponti
• Gebreziher Gidey
• Georg Lamer
• George Lansbury
• Georgii Khorunzhev
• Gerd Puehlhofer
• Guinevere Kauffmann
• Hartmut Scheuerle
• Hermann Brunner
• Hiroshi Nakajima
• HITOSHI NEGORO
• Holger Stiele
• I-Non Chiu
• Ido Reiss
• Ildar Khabibullin
• Ilfan Bikmaev
• Ilkham Galiullin
• Ilya Lomakin
• Ilya Mereminskiy
• Ingo Kreykenbohm
• Iris Traulsen
• Jacob Ider Chitham
• Jann Aschersleben
• Javier Garcia
• Jeremy Drake
• Jeremy Sanders
• Jian Li
• Jiri Svoboda
• Joern Wilms
• johan comparat
• Johannes Buchner
• John Silverman
• John ZuHone
• Jonathan Knies
• Juergen Kerp
• Julien Wolf
• Jürgen Schmitt
• Kirpal Nandra
• Kohei Kobayashi
• Konstantin Postnov
• Konstantina Anastasopoulou
• Konstantinos Migkas
• Labani Mallick
• Laura Lopez
• Lidia Oskinova
• Long JI
• Luca Di Mascolo
• Luigi Costamante
• Manami Sasaki
• Mara Salvato
• Marat Gilfanov
• Marcella Brusa
• Marco Ajello
• Marcus Brüggen
• Marek Kowalski
• Martin Mayer
• Masamune Oguri
• Matteo Guainazzi
• Matthew Graham
• Matthias Klein
• Maurizio Paolillo
• Meicun Hou
• Melanie Lang
• Melih Kara
• Michael Freyberg
• Michael McDonald
• Miriam Elizabeth Ramos Ceja
• Mirko Krumpe
• Murray Brightman
• Naomi Ota
• Natalia Lyskova
• Neven Vulic
• Nhan Nguyen
• Nhut Truong
• Nicholas White
• Nicolas Clerc
• Nobuhiro Okabe
• Norbert Schartel
• Noriko Yamasaki
• Norman Khan
• Ole König
• Paul Giles
• Paul Plucinsky
• Paul Woods
• Pavel Medvedev
• Peter Boorman
• Peter Friedrich
• Peter Jonker
• Peter Predehl
• Philipp Weber
• Qingcui Bu
• Ralph Kraft
• Rana Misato
• Reinout van Weeren
• Riccardo Arcodia
• Riccardo Seppi
• Rodion Burenin
• Roman Krivonos
• rosine lallement
• Ryan Hickox
• SAIKRUBA KRISHNAN
• Sandro Mereghetti
• Santina Piraino
• Sara Buson
• Sara Saeedi
• Satoshi Miyazaki
• Satoshi Nakahira
• Sergey Molkov
• Sergey Sazonov
• Shri Kulkarni
• Sinan ALLAK
• Sotiria Fotopoulou
• Stefan Czesla
• Stefania Carpano
• Stefano Bianchi
• Stefano Marchesi
• Steven Ehlert
• Susanne Friedrich
• Takamitsu Miyaji
• Tanya Urrutia
• Tathagata Saha
• Teng Liu
• Thomas Boller
• Thomas Dauser
• Thomas Kupfer
• Thomas Maccarone
• Thomas Mernik
• Thomas Prince
• Thomas Reiprich
• Tingting Liu
• Tom Shanks
• Tony Mroczkowski
• Tunca Amanvermez
• Veronica Biffi
• Victor Doroshenko
• Victoria Grinberg
• Vincent Eberle
• Vittorio Ghirardini
• Werner Becker
• Werner Collmar
• William Forman
• Xueying Zheng
• Yijun Wang
• Yoshiki Toba
• Zhen-Xuan Liao
• Zhenlin Zhu
Support
• Sunday, March 15
• Registration and Welcome REception
• Monday, March 16
• SRG Instruments and Operations
• 1
Welcome and Introduction
Speaker: Peter Predehl (Max-Planck-Institut für Exteraterrestrische Physik)
• 2
SRG Orbital Observatory: scientific goals and recent results
Speaker: Prof. Rashid Sunyaev (IKI RAS (Moscow), MPA (Germany) )
• 3
SRG Status and Operations
Speaker: Ilya Lomakin (NPOL Lavochkin)
• 4
eROSITA early phase and commissioning operations

The cruise phase of SRG to L2 was used to verify that all eROSITA systems had survived launch and no degradation in the functionality was present. The critical one-time operations of opening the telescope cover and cooling the CCD detectors to -90°C were also carried out during this phase.
This talk presents an overview of the telescope operations during the commissioning phase that verified functionality of thermal and electrical systems and commissioned the CCD cameras before the important Calibration and Pointed Verification phase started. It reports on challenges encountered and summarizes the results from this phase.

Speaker: Diogo Coutinho (MPE)
• 5
The calibration of eROSITA on SRG

The power of eROSITA, the core instrument on the Russian-German SRG mission, is high sensitivity at high spectral, spatial, and temporal resolution over a large field of view. This is achieved by combining 7 coaligned fast X-ray optics, each composed of 54 mirror shells, to focus the X-rays onto a total of 1 million pixels, which can all be used as spectrographs. On their way to the CCDs, the photons have to penetrate optical blocking filters, because X-ray CCDs are also sensitive to optical light. All these components need to be calibrated in order to make full scientific use of the unique capabilities of eROSITA. The initial ground calibration was done at the PANTER and PUMA facilities of MPE as well as at BESSY, and was completed by an in-orbit calibration. We report on the extensive and often challenging calibration activities performed on ground and in space.

• 6
In-flight calibration of the SRG/ART-XC telescope

We present results of extensive calibration program performed with ART-XC telescope during the first months of SRG operation. Performance of the ART-XC detectors was calibrated with use of onboard radioactive source while effective area and
point spread function were verified during observations of bright X-ray sources. The derived detector energy resolution of 9% at 14 keV is in good agreement with ground-based measurements.

Speaker: Ilya Mereminskiy (Space Research Institute RAS)
• 11:00 AM
Coffee Break and Posters viewing
• 7
The eROSITA Near Real Time Analysis

During each ground station contact of Spectrum X-Gamma, about once every 24h, eROSITA data are telemetered to ground and then immediately subjected to a quick scientific and engineering analysis - the Near Real Time Analysis. The purpose of the scientific analysis done by the NRTA is to identify new transient or strongly variable sources which were detected with eROSITA and to monitor sources that are bright enough that they can be observed in a single pass of the instruments. The NRTA creates automated alerts based on a large set of possible source properties, which are then vetted by the NRTA shift team, which then triggers further observations with other facilities and/or publishes the source information.

This presentation gives an overview of the NRTA setup and operations, discusses what phenomena can be uncovered with it, and gives example results from the first months of NRTA operations.

Speaker: Joern Wilms (Remeis-Observatory & ECAP)
• 8
eROSITA data products and data analysis software

The eROSITA Ground Segment team has developed a software package (eSASS - eROSITA Science Analysis Software System) for creating calibrated science data products and for performing various interactive data analysis tasks. The eSASS package builds on experience and in part on code from XMM-Newton and ROSAT, though with significant revisions and upgrades. eROSITA telemetry data received during each daily SRG ground contact are pipeline processed at Max-Planck-Institut für extraterrestrische Physik, creating a set of data products, such as calibrated X-ray event lists, images, exposure, background, and sensitivity maps, as well as X-ray sources catalogs and associated source-level products. These data products are made available to authorized users through a Web interface (details of the data access policy are discussed elsewhere). For in-depth interactive data analysis the eSASS package provides command-line tools performing such functions as data selection, source detection and characterization and the creation of spectra and lightcurves among others. All data products are FITS files complying with established standards such that a range of popular X-ray data analysis tools may be used. The eSASS package interacts with an eROSITA calibration database maintained by the eROSITA team.

Speaker: Hermann Brunner (Max-Planck-Institut für extraterrestrische Physik, Garching)
• 9
Source detection and catalogue construction in SRG/ART-XC sky survey

The overview of SRG/ART-XC data reduction procedures and source detection algorithms will be presented. Efficiency of various source detection methods will be compared using the results of realistic SRG/ART-XC all sky survey simulations. The construction and properties of X-ray source catalogue, obtained from the first months of SRG/ART-XC all sky X-ray survey started on Dec 8, 2019 will be discussed.

Speaker: Rodion Burenin (IKI)
• 10
Timing capabilities of the ART-XC telescope and precision of the on-board clock

We demonstrate here the timing capabilities of the ART-XC telescope
on the time scale from several milliseconds to few seconds. The work was done
based on the data of observations of several pulsars emitting in X-rays. The
observations were carried out during the in-flight Calibration and
the performance verification (PV) phases. Using these data we tested
the stability of the on-board clock and found that the clock is slowing down
with rate approximately 10 ms per day. This lag have been confirmed
also by measurements from the on-ground receiving stations.

Speaker: Dr Sergey Molkov (Space Research Institute, Moscow)
• 11
The eROSITA camera background at L2

We summarize the properties of the eROSITA camera background at L2,
as a function of camera, time, energy, position on detector,
position in orbit, etc.

Speaker: Dr Michael Freyberg (MPE)
• 12
Вackground Measurements by the ART-XC X-ray Detectors near L2 point

The Astronomical Roentgen Telescope – X-ray Concentrator (ART-XC) is one of two X-ray telescopes onboard the SRG mission launched on July 13, 2019 from Baikonur. ART-XC consists of seven co-aligned mirror modules coupled with seven focal plane CdTe double-sided strip detectors. The ART-XC detectors operate in the energy range from 4 keV to over than 100 keV, while the effective area of the ART-XC mirror modules is negligible at energies above 30 keV. In this energy range the ART-XC detectors background is completely determined by the charged particles. We present the results of measurements of the ART-XC detector background near the Sun-Earth L2 point. The detector background was highly stable in the energy range of 40–100 keV during the first few months of SRG operation at the L2 and the background variations did not exceed ±2%. These are the first background measurements by an X-ray detector near L2 point.

Speaker: Dr Alexey Tkachenko (Space Research Institute, Moscow)
• 1:15 PM
Lunch Break
• AGN Surveys and the history of accretion
• 13
The cosmic X-ray background and the history of the growth of black holes

The growth of supermassive black holes (SMBHs) over cosmic time is imprinted in their X-ray luminosity that is emitted from the inner central engine of active galactic nuclei (AGN). Observationally, X-rays from AGN can be probed both through deep and wide X-ray surveys, and also through the integrated emission that makes up the cosmic X-ray background (CXB). I will give an overview of our constraints on SMBH growth from X-ray and multiwavelength surveys and the CXB, focusing on the newest frontiers: AGN at the very dawn of black holes and galaxies (redshift 6 and higher) and AGN that are heavily buried by gas and dust. I will point toward the exciting potential of eROSITA, ART-XC, and future observatories in further uncovering the cosmic growth of SMBHs.

Speaker: Ryan Hickox (Dartmouth College)
• 14
First results on AGN from eFEDS

eFEDS (the eROSITA Final Equatorial Depth Survey) is a CalPV program of the German eROSITA consortium. Using a field-scan observing strategy, eFEDS covers an area of approximately 130 deg^2 in an equatorial field with comprehensive mult-wavelength coverage, notably with Subaaru HSC, VISTA/VIKING and the GAMA spectroscopic survey. With a total exposure time of around 400ks, eFEDS achieves the same nominal depth expected over the whole sky at the end of the 4-year eROSITA all-sky survey. This allows a direct verification and accurate prediction of the expected eRASS X-ray source populations, which are dominated by AGN at high Galactic latitudes such as this. An overview of the first AGN results in eFEDS will be presented.

Speaker: Kirpal Nandra (MPE)
• 15
Multiwavelength properties of eROSITA point-like sources in the eFEDS area

I will present, on behalf of eroAGN and eROFollow-up WGs the multiwavelength counterparts to the eROSITA sources in eFEDS, including their classification (AGN/star). The talk will also cover predictions on our capability to identify the correct counterparts as a function of Ancillary data coverage and depth of X-ray survey (eRASS:1-8).

Speaker: Dr Mara Salvato (MPE)
• 16
ACCRETION HISTORY OF AGN: X-RAY POPULATION SYNTHESIS MODEL & MULTIWAVELENGTH PHOTOMETRIC REDSHIFTS

As matter accretes onto the central supermassive black holes in active galactic nuclei (AGNs), X-rays are emitted. We present a population synthesis model that accounts for the summed X-ray emission from growing black holes; modulo the efficiency of converting mass to X-rays, this is effectively a record of the accreted mass. We need this population synthesis model to reproduce observed constraints from X-ray surveys: the X-ray number counts, the observed fraction of Compton-thick AGNs [log (N_H/cm-2) > 24], and the spectrum of the cosmic X-ray background (CXB), after accounting for selection biases. Over the past decade, X-ray surveys by XMM-Newton, Chandra, NuSTAR, and Swift-BAT have provided greatly improved observational constraints. We find that no existing X-ray luminosity function (XLF) consistently reproduces all these observations. We take the uncertainty in AGN spectra into account and use a neural network to compute an XLF that fits all observed constraints, including observed Compton-thick number counts and fractions. This new population synthesis model suggests that, intrinsically, 50% ± 9% (56% ± 7%) of all AGNs within z ≃ 0.1 (1.0) are Compton-thick.

Speaker: Dr Tonima Tasnim Ananna (Dartmouth College)
• 17
SRGz: cross-match, photometric classification and probabilistic photo-z measurements for X-ray sources in the SRG surveys

We present SRGz - a programming package for doing effective optical cross-match, photometric classification and probabilistic photo-z measurements of SRG extragalactic sources. SRGz is based on competitive empirical machine learning (ML) algorithms: quantile random forest, gradient boosting, deep neural networks. ML-models were trained on SDSS spectral samples of quasars, galaxies and stars and samples of optical sources in the vicinity of X-ray sources from XMM-Newton Serendipitous Source Catalog and can provide accurate photometric prior probabilities for optical counterparts of SRG sources detected during the all-sky survey, their STAR/QUASAR/GALAXY classification scores and photometric redshifts in various forms (photo-z point predictions, confidence intervals and full probability distribution functions PDZ). The proposed methods allow one to precisely identify optical counterparts for the majority of X-ray sources in the SDSS footprint and accurately measure their redshifts with low fraction of catastrophic outliers. Quality of optical cross-match and photo-z prediction models were intensively tested on the spectroscopic X-ray samples in the Stripe82X and XMM-XXL-N extragalactic fields.

Speaker: Dr Alexander Meshcheryakov (IKI)
• 4:25 PM
Coffee Break and Posters viewing
• 18
Tracing the Origin of Seed Black Holes in the Universe

Nearly all galaxies appear to harbor a supermassive black hole. The origin and properties of initial black hole seeds that grow to produce the detected supermassive black hole population are unconstrained at present, as actively growing seeds are not directly observable near their birth epochs. Nevertheless, some unique signatures of seeding survive and can be discerned in: local scaling relations between black holes and their galaxy hosts at low-masses; in high-redshift X-ray and optical luminosity functions of accreting black holes; and in the total number and mass functions of gravitational wave coalescence events from merging binary black holes. I will describe several of these newly proposed observables that encapsulate information about seeding and permit disentangling the confounding effects of subsequent growth, merging and evolution. With exciting prospects for the availability of multi-wavelength (X-ray, Infra-Red, Optical) and multi-messenger data, we stand to trace the origin of the first black holes.

Speaker: Prof. Priyamvada Natarajan (Yale University)
• 19
An optical identification of the SRG sources of the Lockman Hole PV-phase survey

We discuss the first results of the optical identification the SRG X-ray sources of the 18.5 square degrees Lockman Hole PV-phase survey. We show first spectroscopically confirmed quasar candidates at z~4 the spectra of which were obtained at the 1.6-m telescope AZT-33IK and the 6-m telescope BTA.
We review a fraction of optical identification of X-ray sources in the several wide field broad band photometric surveys: SDSS, Pan-STARRS, DESI Legacy Survey.

Speaker: Dr Georgii Khorunzhev (IKI RAS)
• 20
The NEP hard X-ray survey with ART-XC

The Astronomical Roentgen Telescope X-ray Concentrator (ART-XC) instrument onboard the Spectrum Röntgen Gamma (SRG) mission has started the all-sky hard X-ray survey since 2019/12/08. The observations of the ecliptic pole regions will reach exceptional depth thanks to the survey design of overlapping exposure in these regions. In anticipation of the ART-XC survey in the North Ecliptic Pole (NEP) region, we explore publicly available multiwavelength catalogs in the NEP region and investigate AGN candidates that might exhibit hard X-ray signals that will be detected by ART-XC. To capitalize on the ART-XC coverage in the NEP region, we also investigate ART-XC cadence and sensitivity limits for a selected few luminous X-ray sources. Comparisons between our simulations and the ART-XC survey in NEP will also be discussed.

Speaker: Dr Chen Chien-Ting (NASA MSFC/USRA)
• 21
AGN identification with machine-learning methods

Several pieces of evidence have been pilling up in the literature leading towards an evolutionary scenario for AGN, moving past the standard unified model. Part of this amounting evidence is the little overlap of AGN samples selected with various identification criteria. Given the rarity of the AGN population, large and complete samples are needed to assess such an evolutionary model and clarify the growth of black holes and a potential coevolution with their host galaxies.

X-rays are undoubtedly an optimal AGN identification method as revealed by XMM-Netwon, Chandra, and now eROSITA. However, deep all sky surveys such as LSST and Euclid will provide at least one order of magnitude larger galaxy samples compared to the most optimistic predictions of eROSITA. I will present three recent approaches using multiwavelength datasets tailored to identify AGN with machine-learning methods. These methods have been developed and tested on available optical, near infrared and X-ray public datasets and will reach their true potential with the combined power of LSST, Euclid and eROSITA.

Speaker: Sotiria Fotopoulou (University of Bristol)
• 22
Optical identifications of SRG X-Ray sources by using RTT-150 observations

In this report we will present first results of the optical identifications by using 1.5-m Russian-Turkish telescope of the sample of X-Ray sources detected with eRosita and ART-XC onboard SRG in the Lockman Hole region during PV period in November 2019. We will inform also results of SRG orbit's astrometric support observations by using RTT-150 in the period July 2019 - February 2020.

Speaker: Prof. Ilfan Bikmaev (Kazan Federal University, Kazan, Russia)
• Tuesday, March 17
• Clusters and Cosmology I
• 23
ICM physics: how to use clusters for cosmology

eROSITA mission will soon produce an unprecedented number of galaxy clusters, which in turn should help improve X-ray based cosmological measurements. However, in order to use the eROSITA data for precision cosmology, we must improve our understanding of the physics of X-ray emitting intracluster medium (ICM) and develop techniques to control associated systematic uncertainties in cluster mass estimates. In this work, I will discuss (1) recent advances in our understanding of ICM physics and cluster mass estimation based on hydrodynamical simulations and X-ray and microwave observations and (2) strategies to improve both cluster astrophysics and cosmology using the forthcoming eROSITA data.

Speaker: Prof. Daisuke Nagai (Yale University)
• 24
From eFEDS to the All Sky Survey: Cluster Science and Cosmology with eROSITA
Speaker: Dr Esra Bulbul (MPE)
• 25
Characterization of the X-ray properties of the eFEDS detected Clusters

Constraints on cosmology from cluster number count strongly depend on the accuracy of cluster masses which are sensitive to the dynamical state of clusters, thus it is of importance to be able to measure accurately the dynamical state of each cluster. eROSITA telescope on board of Spectrum-Roentgen-Gamma (SRG) mission was launched in July 2019. eROSITA's large effective area, good spatial resolution, and a large field of view allow observing large areas of the sky. eROSITA Final Equatorial Survey, the largest contiguous, uniformly sampled X-ray field scan to date was completed in just 4 days during the Performance Verification phase. We found more than 400 extended sources in the 140 square degree eFEDS field. In this talk, we will present the measurements of several morphological parameters: surface brightness concentration, ellipticity, cuspiness, power ratios, and photon asymmetry of eFEDS extended sources. The fractional number of clusters with cool-core/non-cool-cores will allow us to investigate the distribution of the morphological parameters with respect to their mass and dynamical state.

Speaker: Vittorio Ghirardini (Max Planck Institute for extraterrestrial physics)
• 26
Optical confirmation of eROSITA selected clusters

X-ray surveys such as those conducted by eROSITA are a powerful way to identify large
numbers of galaxy clusters. But cluster candidates identified by eROSITA need additional confirmation and redshifts to provide a clean cluster catalog that can be used for science.
Modern optical imaging surveys such as HSC, DES and the Legacy Survey cover large fractions of the eROSITA extragalactic sky and provide depths that are sufficient to identify eROSITA clusters out to z~1.1.
In this talk we present methods and first results of the optical identification of eROSITA clusters.
The main focus of this presentation will be on the confirmation, redshift estimation and measurement of the basic optical properties of cluster candidates found in the eROSITA Final Equatorial-Depths Survey (eFEDS).

Speaker: Matthias Klein (LMU)
• 27
Comparing Hydrostatic and Dynamical Masses of Clusters of Galaxies

Accurate and precise mass measurements of clusters of galaxies are critical for constraining cosmology with cluster number counts from eROSITA. Much progress has been made in measuring cluster masses from X-rays (assuming hydrostatic equilibrium), weak gravitational lensing, and galaxy dynamics, but systematic differences between the methods still remain at the tens of percent level. We will present the largest comparison between cluster masses determined from X-ray hydrostatic analyses and galaxy dynamics using the caustic method. In a sample of 44 galaxy clusters we find evidence for a significant systematic difference with the hydrostatic masses being higher than the caustic masses by about 30% on average. We discuss possible reasons for this effect.

Speaker: Ben Maughan (University of Bristol)
• 28
Simulating clusters and their AGN with IllustrisTNG

The IllustrisTNG simulations produce an unprecedented sample of thousands of well-resolved galaxies within halos of total mass above 10^13 solar masses. TNG is a series of gravo-magnetohydrodynamical cosmological volumes which enable us to simultaneously resolve the internal structure of galaxies at ~hundred parsec scales, while also capturing the full diversity of entire galaxy populations. The comprehensive, physical model captures a detailed view of the physical interaction between AGN feedback and the hot gaseous atmospheres of these objects, and the influence of the black holes is imprinted on the thermodynamical properties of the gas within and around clusters. I will showcase what we are learning about the stellar mass assembly and quenching of cluster galaxies, as well as their black hole and AGN populations. I will discuss the emergence of cool core and non-cool core cluster populations, as well as the abundance and distribution of x-ray tracing OVII and OVIII in cluster atmospheres. I will connect the physical operation of the galaxy formation model, primarily through the impact of black hole feedback, to x-ray scaling relations and the x-ray properties of halos, and comment on the ability for simulations like IllustrisTNG to make quantitative predictions for eROSITA observables, as well as the potential for the mission to constrain many key aspects of the theoretical models currently employed in cosmological hydrodynamical simulations.

Speaker: Dr Dylan Nelson (MPA)
• 10:50 AM
Coffee Break and Posters viewing
• 29
Cluster Surveys and Cosmology with the Sunyaev-Zel'dovich Effect

I will give an overview of Sunyaev-Zel'dovich (SZ) cluster surveys, the resultant cosmological constraints, and projected future results. Since the first SZ-discovered cluster in 2008, there are now over 1500 SZ-selected clusters reported in the literature. Ongoing surveys from AdvACT and SPT-3G promise to deliver samples with several thousand additional clusters in the next few years, with the future CMB-S4 experiment expected to find over 100,000 clusters. These data sets promise to deliver unique samples of massive clusters at z > 1, including proto-clusters detected at z > 4 from their mm-wave emission The resultant cosmological constraints from the cluster number density will require an understanding of the cluster selection and mass calibration, which will rely on multi-wavelength data from overlapping X-ray and optical surveys that will enable additional cosmological studies. I will summarize these upcoming results, challenges, and projected cosmological constraints.

Speaker: Bradford Benson (Fermilab, University of Chicago)
• 30
Unravelling Galaxy Cluster Evolution with Combined SZ & X-ray Surveys

The recent combination of deep Sunyaev Zel'dovich (SZ) surveys with pointed X-ray follow-up has enabled the study of the intracluster medium across most of cosmic time. In particular, within the South Pole Telescope (SPT) collaboration, we have been utilizing Chandra and XMM-Newton follow-up of SPT-selected clusters to study the evolution of the dynamical state, the cooling/heating balance, and the metal enrichment of the intracluster medium over the past 10 Gyr. I will briefly summarize these results, before describing the numerous synergies of SPT-3G and eRosita, and previewing how these combined observatories will further unravel the complex history of the intracluster medium.

Speaker: Michael McDonald (MIT)
• 31
The hot gas at the edge of galaxy clusters and beyond: from simulations to X-ray observations

The properties of the hot medium at the periphery of galaxy clusters and in filaments connecting cosmic structures carries crucial information on their accretion history and on the feedback and enrichment processes from galaxies. In order to study the details of these processes and the three-dimensional structure of the diffuse baryons in clusters and cosmic filaments we resort to large cosmological hydrodynamical simulations, whose predictions can be directly compared against observational data.
We focus in particular on multiple systems of interacting galaxy clusters, obtained from light-cones extracted from the Magneticum simulation suite. I will discuss preliminary results and comparisons with observations of real systems, such as the A3391/95 pair observed with eRosita, by means of realistic mock eRosita observations generated from the simulated candidates. With this strategy, we aim at constraining the l.o.s. structure of similar systems from the X-ray properties, as well as the thermo-dynamical and chemical features of the gas between the member clusters.
Such realistic study of mocks from simulations is a fundamental complementary step given the large statistics provided by the eRosita survey, that can possibly lead to the identification of other candidates and to the study of the low surface-brightness gas at cluster boundaries and in filaments/bridges via stacking analyses.

Speaker: Veronica Biffi (University Observatory Munich (Germany))
• 32
The chemical history of galaxy clusters, groups, and ellipticals - Advances from previous missions and insights with eROSITA

Although they are the building blocks of rocky planets and even life, the major fraction of metals in the Universe is found outside galaxies, within a hot, ionized intergalactic phase. When this plasma is hot and dense enough to glow in X-rays (i.e. pervading galaxy clusters, groups, and surrounding isolated elliptical galaxies), the abundance of key chemical elements can be measured via spectroscopy; hence providing us with crucial clues on the chemical history and evolution of large scale structures. In particular, past X-ray missions revealed that the bulk of metals in the intracluster medium was already in place before cluster formation, i.e. more than ~10 Gyr ago. In hot atmospheres pervading galaxy groups and ellipticals, however, the picture is less clear and many open questions remain. Whereas microcalorimeters onboard future missions (e.g. XRISM, Athena) will certainly bring a plethora of decisive results, moderate resolution spectroscopy combined with an unprecedented grasp has the potential to considerably improve our current knowledge of how and when these systems got chemically enriched. Here, we will review some of the most important results achieved with XMM-Newton, Chandra, and Suzaku, and we will show how (and on which aspects) eROSITA can push our understanding of galaxies and clusters enrichment to the next level.

Speaker: Francois Mernier (European Space Agency / ESTEC)
• 33
Unraveling the origin of non-thermal phenomena in merging galaxy clusters with eROSITA, LOFAR, and Planck

Mergers between galaxy clusters are the most energetic phenomena in the Universe. During these cosmic collisions, turbulence and shocks are generated into the ICM where they are believed to power Mpc-scale diffuse synchrotron sources in form of radio halos and radio relics. Nowadays, studies on non-thermal phenomena in merging galaxy clusters have been limited to a few tens of massive systems (M500 > 5-6 x 10^14 Msun), which host the most powerful halos and relics. Thanks to the all-sky surveys performed with eROSITA, LOFAR, and Planck, we will finally be in the position to extend these studies over a broad range of cluster mass and redshift and thus to unravel the origin of radio diffuse sources in the ICM.
The Planck Sunyeav Zel'dovic catalog collects a nearly mass-selected sample of galaxy clusters. We are carrying out the analysis of LOFAR observations coming from LoTSS (that is an on-going radio survey aimed at imaging the entire northern sky at 120-168 MHz) of all these systems to perform the largest statistical study ever done on non-thermal phenomena in galaxy clusters. However, many of the Planck clusters do not have X-ray information available at the moment. In this respect, the eROSITA survey will have a critical role, allowing us to understand the dynamical state of the clusters and thus to study the occurrence of diffuse radio emission in merging galaxy clusters.
In my talk, I will present the current status of the LOFAR analysis based on ~300 Planck clusters observed in the context of LoTSS. A large fraction of these systems host diffuse radio sources in the ICM, for the very first time detected in low-mass (M500 < 5 x 10^14 Msun) and high-z (z>0.6) systems. These clusters are fundamental to test the theoretical models of the formation of halos and relics. The eROSITA survey will detect these systems, which are below the sensitivity of the ROSAT All-Sky Survey, allowing us to study the interplay between thermal and non-thermal components in the ICM.

Speaker: Dr Andrea Botteon (Leiden Observatory)
• 34
The eROSITA view of the merging cluster Abell 3266

Abell 3266 is a fascinating merging galaxy cluster system, showing a great deal of substructure. There is a plume of low entropy gas running from the core of the cluster, which may be material stripped from a subcluster (Sauvageot et al. 2005; Finoguenov et al. 2005). eROSITA observed A3266 as a calibration target. The wide field of eROSITA and uniform coverage provide an excellent opportunity to study the cluster in detail and understand the merging process. We examine the temperature, metallicity and surface brightness distributions in the core of this cluster. By comparison with simulations, and using mutliwavelength datasets, we discuss the most likely scenarios which took place to form the cluster seen today.

Speaker: Jeremy Sanders (MPE)
• 1:10 PM
Lunch Break
• Clusters and Cosmology II
• 35
The ICM: synergies between radio and X-ray observations of clusters

In a growing number of galaxy clusters diffuse extended radio sources have been found. The radio emission implies the presence of cosmic rays and magnetic fields in the intracluster medium (ICM) on megaparsec scales. An important question is how the cosmic rays are accelerated that produce these extended synchrotron emitting sources. It is generally believed that shocks and turbulence play an important role in the acceleration of these cosmic rays. In this talk I will provide an overview of the synergies between radio and X-ray observations of clusters to understand the nature of the non-thermal ICM components.

Speaker: Reinout van Weeren (Leiden University)
• 36
Large scale view of the Abell 3391/95 multiple galaxy cluster system

We present the large-scale multi-wavelength view of the nearby (z~0.05) Abell 3391/95 multiple galaxy cluster system. We have obtained (i) the first deep (~10 ks nominal) large-area (~10 sq.deg) high-quality X-ray data using eROSITA in scan mode during its Performance Verification Phase; (ii) an even larger scale sensitive (~30 uJ) radio continuum image obtained with ASKAP as part of the EMU Early Science observations; (iii) dedicated DES-depth DECam pointed observations covering the full eROSITA scan region. The eROSITA data reveal in detail the gas bridge connecting the A3391 cluster and the A3395n/s double cluster as well as a number of infalling matter clumps surrounding the entire system, and, of course, many background AGN, galaxy groups, and clusters. Relativistic plasma from a variety of sources is detected in the ASKAP image, including wide angle tail galaxies tracing relative motions to the hot gas in the system, and possible radio relics. Those structures are traced by the galaxy distribution as characterized in the deep multicolor DECam images. Here, we provide an overview of the data and first science results.

Speaker: Prof. Thomas Reiprich (Argelander-Institut für Astronomie, Universität Bonn)
• 37
eROSITA spectral analysis of the A3391/95 filament region

Abell 3391/3395 is a pair of galaxy clusters at z=0.05. The clusters A3391, A3395, and a galaxy group located between the two clusters are in alignment along a large-scale filament. The previous studies by ASCA, ROSAT, Planck, Suzaku, and Chandra indicate and confirm that A3395 and A3391 are connected by the filament with hot diffuse gas. The eROSITA first-light observation of A3391/95 has been conducted, whose deepest X-ray data enable us to constrain the properties of warm (~2e6 K) and hot gas components in the filament. In this presentation, we report early results of spectral and image analyses of the filament region.

Speaker: Naomi Ota (AIfA)
• 38
The SRG/eROSITA view of the Coma cluster

One of the X-ray brightest clusters – A1656 (Coma) – was observed during the PV program for 2 days covering the cluster up to its virial radius and beyond. We will present the results of imaging and spectral analysis of these data and immediate implication for the cluster studies with SRG/eROSITA.

Speaker: Dr Eugene Churazov (IKI/MPA)
• 39
The Coma-NGC 4839 merger scenario in the light of new SRG/eROSITA data
Speaker: Natalia Lyskova (IKI (Moscow))
• 4:00 PM
Coffee break and Posters viewing
• 40
The Atacama Large Aperture Submm Telescope (AtLAST): A widefield, ground-based complement to eROSITA

The thermal and kinematic SZ effects provide a strong and independent complement to X-ray observations of the warm and hot ionised intracluster and intergalactic media, particularly at high redshift where X-ray counts are limited. Being observable from the ground, new instrumentation for the SZ effects can be developed more rapidly and can be upgraded more readily. I will discuss a newly proposed research infrastructure, which has a high profile in the US Astro2020 decadal and Canadian Long Range Plan 2020 submissions as well broad international support, for a 50-meter-class widefield submm/mm telescope capable of observing the multifaceted SZ effect and disentangling it from contaminating radio and dusty submm sources. This will provide 10$^{\prime\prime}$ resolution at 150 GHz (near the peak of the thermal SZ decrement) and a 2 degree instantaneous field of view.

Speaker: Tony Mroczkowski (ESO)
• 41
X-ray spectroscopy of the outskirts of the Perseus Cluster: a shock front near the virial radius

Previous X-ray studies of the Perseus Cluster, consisting of 85 Suzaku pointings along eight azimuthal directions, revealed a particularly steep decrease in the deprojected temperature profile near the virial radius r_{200} along the northwest (NW). We have investigated four additional Suzaku observations mapping this region, with a total exposure of ~100 ks. With this deeper data set, designed to have the best possible control of systematic uncertainties, we find that the temperature gradient is indeed much larger than the other seven directions and significantly deviates from the predictions from hydrodynamic simulations. It is noteworthy that the slope of the deprojected temperature profile is not continuous, with a break near r_{200}.We also find a corresponding density jump at a radius of 1.8 Mpc, similar to the location of the temperature break, indicating the presence of a shock front. This potential evidence of a shock front so far away from the cluster center is unprecedented, and may provide a first insight into the properties of large-scale virial shocks which shape the process of galaxy cluster growth. This study serves as a pathfinder for more such features that may be revealed in nearby galaxy clusters, taking advantage of eROSITA’s large field of view, stable background, and improved spatial resolution compared to Suzaku.

Speaker: Ms Zhenlin Zhu (SRON/Leiden University)
• AGN physics, variability, clustering
• 42
eROSITA AGN simulations and preliminary clustering analysis

In this talk (could also be a poster) I will present a model of how active galactic nuclei populate the cosmic web (detailed in Comparat et al. 2019).
Then I will show preliminary results on the observed angular clustering of point sources in the eROSITA eFEDs PV observations.

Speaker: Johan Comparat (MPE)
• 43
Unexpected eROSITA spectra of Active Galactic Nuclei

The first large area survey of eROSITA unveiled a small set of Active Galactic Nuclei with unusually steep and flat spectral slopes. In the calibration period and the all-sky survey eROSITA also revisited well-known X-ray sources. We report on an automated detection of spectral changes in the X-ray sky compared to archival observations, based on the XMM-Newton, Chandra and Swift archives. The bona fide differences can be grouped into 1) drastic steepening of the intrinsic corona power law and 2) occultation of the corona by an intervening cloud. We will discuss the underlying physics and how to probe them through follow-up with X-ray and optical telescopes. The large-scale eRASS monitoring for occultation events in particular are a promising tool to constrain the granularity of the nuclear obscurer.

Speaker: Johannes Buchner (MPE)
• 44
eROSITA discovery of a new AGN state in 1H0707-495

One of the most prominent AGNs, the ultrasoft Narrow-Line Seyfert 1 Galaxy 1H0707-495, has been observed with eROSITA as one of the first CAL/PV observations on October 13, 2019 for about 60.000 seconds. 1H 0707-495 is a highly variable AGN, with a complex, steep X-ray spectrum, which has been the subject of intense study with XMM-Newton in the past. 1H0707-495 entered an historical low hard flux state, first detected with eROSITA, never seen before in the 20 years of XMM-Newton observations. In addition ultra-soft emission with a variability factor of about 100 has been detected for the first time in the eROSITA light curves. We discuss fast spectral transitions between the cool and a hot phase of the accretion flow in the very strong GR regime as a physical model for 1H0707-495, and provide tests on previously discussed models.

Speaker: Prof. Thomas Boller (MPE)
• Wednesday, March 18
• AGN and their host galaxies
• 45
The relationship between growing SMBHs and their host galaxies

Determining which conditions within galaxies enhance or reduce central SMBH growth is challenging. AGN variability can wash out underlying correlations between galaxy and AGN properties, while AGN selection biases further complicate the observational picture. I will present recent work that addresses these issues, using deep Chandra X-ray data and stellar mass-selected galaxy samples to determine the full distribution of AGN accretion rates within the galaxy population. We trace how the AGN incidence changes as a function of both stellar mass and star formation rate over the bulk of cosmic time (z~0.1-4). We find that within the star-forming population there is a stellar mass dependence to AGN activity; however, no such dependence is seen within the quiescent population. We show that the incidence of AGN within star-forming galaxies on the main sequence is correlated with their SFR, indicating that AGN activity is primarily related to the amount of cold gas in a galaxy. However, we also see that galaxies below the main sequence have a higher AGN incidence, indicating that a broader range of mechanisms are responsible for the triggering and fueling of AGN across the full galaxy population.

Speaker: Prof. Alison Coil (UC San Diego)
• 46
X-ray signatures of black hole feedback: theory confronts observations

State-of-the-art cosmological simulations of galaxies and galaxy clusters, such as IllustrisTNG (www.tng-project.org), suggest a scenario whereby the quenching of star formation in massive galaxies is caused by gas removal from the central regions of galaxies, in addition to gas heating, because of the activity of super massive black holes. The IllustrisTNG project comprises a series of large-volume cosmological simulations where gravity, magnetohydrodynamics and prescriptions for star formation, stellar evolution, metal enrichment, cooling and heating of the gas, galactic outflows and feedback from the supermassive black holes (SMBHs) are all taken into account within the LCDM paradigm. In practice, in these simulations, with one unique set of physical ingredients, we simultaneously resolve and model the inner structural details of thousands of galaxies across 5 orders of magnitude in stellar mass, across environments, and together with the evolution and dynamics of the inter-stellar, circum-galactic and inter-galactic media. The phenomena emerging from the underlying effective theory for galaxy formation include an observationally-consistent separation of star-forming and quenched galaxies across a wide range of observables across cosmic epochs. In this talk, I will focus on a specific, quantitative prediction by IllustrisTNG and its test against observational data. On the one hand, according to the IllustrisTNG simulations, star-forming and quiescent galaxies exhibit markedly distinct X-ray luminosity vs. K-band magnitude relations. In particular, the IllustrusTNG simulations predict a clear X-ray luminosity separation between star-forming and quiescent galaxies at M_K~ −24, corresponding to stellar masses of 10^10.5-10.7 solar masses, with star-forming galaxies being X-ray brighter than their quenched counterparts, by up to two orders of magnitudes (Truong, Pillepich et al. 2019). The difference is more prominent within the central regions (< Re) than at larger radii (<5Re) and it is qualitatively broadly consistent with currently available X-ray data of late and early-type galaxies in the local Universe. On the other hand, --if everything goes fine -- I will use data collected by eROSITA during the Science Verification phase and targeting galaxies from the Hyper Suprime Camera surveys with Subaru to perform more robust and extensive tests for the L_X dichotomy predicted insofar and hence to further probe the quenching mechanism in the Universe.

Speaker: Annalisa Pillepich (MPIA Heidelberg)
• 47
Structural properties of the host galaxies of eROSITA AGN with Subaru/HSC

The growth history of supermassive black holes is known to be influenced by their environment from the host galaxy to larger scale structure. However, the direct physical mechanisms involved are not fully understood. The wide imaging, depth, and superb spatial resolution of the Subaru Hyper-Suprime Cam Strategic Survey Program provides the opportunity to make significant progress. For instance, the imaging is enabling the structural properties of luminous AGN to be measured up to z ~ 1. We will present the size and light profile analysis (i.e., Sersic indices) of the hosts of eROSITA AGNs with a comparison to normal galaxies both star-forming and quiescent at equivalent redshifts and stellar masses. These results establish whether most black hole growth occurs in galaxies also forming stars on specific physical scales (disk vs. bulge). We will also touch upon related eFEDS efforts: (1) the morphological analysis of the full galaxy population in eFEDs for studies of environmental effects using eFEDS clusters as an environmental indicator, and (2) galaxy-galaxy lensing to quantify where within dark matter halos AGNs prefer to reside.

Speaker: John Silverman (Kavli IPMU)
• 48
AGN feedback: lessons learned from X-ray surveys and prospects for eROSITA

Outflowing winds are now revealed routinely in Active Galactic Nuclei and Quasars across the entire electromagnetic spectrum and are invoked in many co-evolutionary models to link the growth of SMBH and galaxies through feedback phenomena. Both numerical simulations and observations have shown that the nature of AGN outflows is multiphase, and that each gas phase embeds a fundamental piece of information on the driving mechanism and on the effect on the host galaxy.
I will present recent results on the detection of strong winds at different scales through dedicated NIR and ALMA follow-ups of luminous obscured AGN, and the implications for AGN/galaxy co-evolution. I will discuss the unique power of AGN X-ray surveys (coupled with deep optical-NIR surveys) in selecting the most promising targets. I will finally discuss the perspectives for the forthcoming eROSITA survey to advance in our understanding of these important phenomena, based on preliminary results of the PV phase observations in the eFEDS field covered by HSC and VIKING.

Speaker: Marcella Brusa (DIFA - University of Bologna)
• 49
eFEDS view of WISE 22 $\mu$m-selected galaxies/AGNs collaborated with Subaru Hyper Suprime-Cam

We present physical properties (e.g., X-ray luminosity and hardness ratio) of WISE 22 $\mu$m-selected galaxies/AGNs. Using a latest eFEDS X-ray point source catalog with optical and mid-infrared (IR) counterparts, we made a sub-sample of 2102 objects with S/N (22 $\mu$m) > 5.0. After removing possible stars, we cross-identified with KiDS, VIKING (near-IR), and H-ATLAS (far-IR) catalogs, which yielded 268 objects at $0 < z < 2.5$ in $\sim$50 deg$^2$. Photometric redshift of some objects are estimated based on the Hyper Suprime-Cam on the Subaru telescope. We derived their stellar mass, star formation rate (SFR), AGN 6 $\mu$m luminosity ($L_{\rm 6}^{\rm AGN}$), and IR luminosity ($L_{\rm IR}$) based on spectral energy distribution fitting with CIGALE. We also estimated their 2-10 keV luminosity ($L_{\rm X}$) and hardness ratio (HR). We found that about 20% of objects are expected to be hyperluminous IR galaxies with $L_{\rm IR}$ > 10$^{13}$ $L_{\odot}$. Their stellar mass-SFR relation would suggest that they have an active star-formation regardless of their redshift. We confirmed a tight correlation between $L_{\rm 6}^{\rm AGN}$ and $L_{\rm X}$, and about 15% of objects are expected to be moderately obscured population with hydrogen column density ($N_{\rm H}$) > 10$^{23}$ cm$^{-2}$, which is roughly consistent with what is inferred from HR.

Speaker: Dr Yoshiki Toba (Kyoto University)
• 50
The local AGN survey (LASr): Towards a complete census of black hole growth within 100Mpc

In order to answer some of the major open questions in the fields of supermassive black hole (SMBH) and galaxy evolution, a complete census of SMBH growth, i.e., active galactic nuclei (AGN), is required. Thanks to the combination of the new deep all-sky surveys, such as those by the Wide-field Infrared Survey Explorer (WISE) and the Spectrum-Roentgen-Gamma (SRG) missions eROSITA and ART-XC, this task is now becoming feasible in the nearby Universe. We present a new survey, the Local AGN Survey (LASr), with the goal of identifying AGN unbiased against obscuration and determining the intrinsic Compton-thick (CT) fraction. As part of LASr, we have assembled the most complete all-sky sample of galaxies within 100Mpc from astronomical databases, four times deeper than the current local galaxy reference, the Two Micron All-Sky Survey Redshift Survey (2MRS), which turns out to miss ~20% of known luminous AGN. This galaxy sample will serve as parent sample to select AGN. We assemble and characterise all 4.3k known AGN within the volume and employ infrared colour selection to find new AGN candidates independent of their obscuration. The fact that none of these candidates have been detected by Swift/BAT yet indicates that the CT fraction is in the range of 40-55%. We estimate the efficiency of the infrared colour selection and use it to predict the total number of AGN in the volume, finding that a third of the objects are still undetected. Thanks to the deep flux limits, the all-sky surveys of eROSITA and ART-XC are going to detect many of these sources, while putting tight constraints on those that remain undetected and thus be CT. These X-ray information will be highly complementary to the infrared and help to overcome selection biases of the latter. Thus, the combination of infrared and X-ray selection of AGN is the best approach to obtain an unbiased and complete census of (significant) black hole growth in the local universe. Such a census will serve as redshift zero benchmark for AGN population studies, providing constraints on the AGN duty cycle, luminosity and accretion rate distributions and radiative efficiencies.

Speaker: Daniel Asmus (University of Southampton)
• 10:45 AM
Coffee Break and Posters viewing
• X-ray emission from Galaxies
• 51
X-ray Surveys and the Evolution of Normal Galaxy Emission: Prospects for eROSITA

Surveys of the extragalactic Universe, from ultraviolet to infrared
wavelengths, have been extremely effective at piecing together a basic picture
of how stars in galaxies evolved throughout cosmic history. At X-ray
wavelengths, normal-galaxy emission (i.e., not due to AGN) is dominated by hot
gas and populations of X-ray binaries (XRBs). eROSITA is expected to detect
~10,000 normal galaxies in X-rays, much larger than the populations of 100s of
normal galaxies that are currently studied in X-ray surveys. In this talk, I
will review recent efforts to establish an empirical framework that
characterizes how the X-ray emission from normal-galaxy populations varies with
galaxy properties like star-formation history and metallicity. I will present
estimates of how the X-ray emission from galaxies likely evolved over cosmic
time in response to changes in galaxy star-formation activity and metallicity.
I will show that X-ray emissivity of the Universe at z > 4-6 is expected to be
dominated by normal-galaxy populations and could provide significant heating of
the early intergalactic medium (IGM) before the epoch of reionization in the
Universe. Finally, I will discuss how eROSITA will help to fill important
knowledge gaps in our empirical framework, and provide broader new insight into
galaxy evolution and the X-ray radiation field of the early IGM.

Speaker: Bret Lehmer (University of Arkansas)
• 52
Surveys of Normal Galaxies at harder X-ray energies with NuSTAR

Since its launch in 2012, NuSTAR, as the first imaging X-ray observatory to operate in the 3-80 keV band, has executed an observing program on normal and starburst galaxies, including several galaxies in the Local Group, through a combination of science team, Legacy project, and Guest Observer time. We report on recent results from a synthesis analysis of a dozen galaxies observed by NuSTAR, including an analysis that divides X-ray binaries by compact object type (neutron star vs black hole), and measurement of the overall hard X-ray SED of galaxies. We have found a nearly universal turnover in the hard X-ray SED that may be attributed to super-Eddington accretion onto ULX sources. We have also found that the NS Luminosity function may have a turnover near the Eddington limit for a 1.4 solar mass NS. We discuss our findings on NS/BH ratios in galaxies and prospects for the future. In closing, we touch upon follow up in the harder X-ray band by NuSTAR and successor facilities of interesting subclasses of eROSITA-observed galaxies.

Speaker: Ann Hornschemeier (NASA GSFC)
• 53
XMM-Newton survey of star-forming galaxies in the local Universe: X-ray binary scaling relations

We present an analysis of the X-ray properties of all galaxies within a radius of 200 Mpc observed with XMM-Newton. These galaxies are the result of cross-correlation between the XMM-Newton archive and the HECATE catalogue, the most complete galaxy catalogue of the local Universe incorporating robust distances and stellar population parameters. In our analysis we use data from all objects observed by XMM-Newton (3041 galaxies). The sample spans 5 dex in star-formation rate and 4 dex in stellar mass and includes objects with no formal detections (i.e. upper limits). Furthermore, we perform detailed spectral fitting for all galaxies with adequate number of counts (1713 galaxies), in order to measure their spectral parameters and to identify the AGN in our sample. Using the largest X-ray sample of galaxies available so far, we measure the parameters of the linear relations between X-ray luminosity, star-formation rate, and stellar mass. We find a good agreement with previous works, but the great increase in the sample results in a larger scatter possibly due to age and metallicity differences of the stellar populations. This is an excellent reference sample for eROSITA surveys of normal galaxies as well as AGN. eROSITA will provide a truly unbiased sample for studies of galaxy scaling relations, which combined with the HECATE catalogue will allow us to derive the ultimate scaling relations for galaxies of different types and metallicity, measure their dependence on these parameters, and address the origin of the observed scatter.

Speaker: Konstantina Anastasopoulou (University of Crete/FORTH)
• 54
X-ray emission from starburst dwarf galaxies: galactic winds and X-ray binaries

Low mass, low metallicity starburst galaxies are of special interest for galaxy evolution, since they are not only laboratories for massive star evolution and feedback at low metallicity, but also the extreme end of energy input into a galacitic potential. In many ways they are the best proxies for the z ~ 6 to 10 protogalaxies, which are inaccessible to detailed observational studies.
The observation of X-ray emission is crucial for understanding the workings in these dwarf starburst in two ways, firstly to map and analyze the properties hot gas in galactic outflows and winds, and secondly as hosts of a massive X-ray binaries population which contributes significantly to the radiation field in these galaxies. In this talk I will present results of XMM-Newton and Chandra analyses of local and intermediate redshift dwarf starburst galactic winds and X-ray binaries and put them into context with our new VLA and LOFAR on the importance of magnetic fields for the outflows and LBT spectroscopy on dwarf starbursts with very hard radiation fields.
I will also provide a outlook toward the use of eROSITA for the large scale mapping of hot gas of galactic winds and the impact of luminous X-ray binaries for the ionization field in low metallicity starburst galaxies.

Speaker: Dominik Bomans (Astronomical Institute of the Ruhr University Bochum)
• 55
High mass X-ray binaries in the Magellanic Clouds as seen by eROSITA during the Commisioning/Calibration phase

High mass X-ray binaries (HMXBs) offer a unique opportunity to study the physics of accretion in extreme environments and magnetic fields. In these systems, matter is accreted from a massive star onto a compact object which is usually a neutron star. A large number of HMXBs is found in the Magellanic Clouds, especially in the Small Magellanic Cloud (SMC). This is attributed to their ideal environment for hosting young stellar remnants, high formation efficiency for HMXBs, as well as relatively small distances and low foreground absorption conducive for performing detailed studies. This enables us to study HMXBs in the Magellanic Clouds down to a point source X-ray luminosity of a few 10^33 erg/s. We will present the first results from the few HMXB pulsars in the Magellanic Clouds that were in the field of view during the eROSITA calibration and commissioning phase observations including a new X-ray pulsar. We will discuss their spin evolution and spectral properties in the context of accretion onto highly magnetized neutron stars.

Speaker: Chandreyee Maitra (MPE)
• 56
All-sky X-ray maps with MAXI/SSC

We will present diffuse X-ray background maps obtained with Solid-state Slit Camera (SSC) on board the MAXI mission for 2 years from 2009 to 2011, in energy bands of 0.7-1.0, 1.0-2.0, and 2.0-4.0 keV (arXiv:1912.01572). They are the first ones that were derived with a solid-state instrument, and to be compared with the previous ROSAT all sky survey result. While the SSC map in the highest energy band is dominated by point sources and the Galactic Diffuse X-ray emission, that in 0.7-1.0 keV reveals an extended X-ray structure, of which the brightness distribution is very similar to that observed with ROSAT about 20 years before. The SSC map suggests a fainter and larger ellipse, which is elongated in the north-south direction and roughly centered at the Galactic center. The spectrum of these structures is explained as thin thermal emission from a plasma, with a temperature of ~0.31 keV and an abundance of ~0.3 Solar. Based on SSC observation conditions including the low Solar activity, the Solar Wind Charge Exchange signals are estimated to be negligible in the present SSC maps, as well as in the >0.56 keV ROSAT map.

Speaker: Satoshi NAKAHIRA (ISAS/JAXA)
• Thursday, March 19
• X-ray view of the Milky Way: Stars
• 57
The Future of High Energy Stellar Physics

eROSITA is poised to unleash a deluge of information on the stellar X-ray sky in a nexus with other powerful complementary missions and capabilities, such as TESS, Gaia and LSST. I will endeavour to provide a brief overview of the outstanding problems in high energy stellar physics, and the status of our knowledge deep into the Chandra and XMM-Newton era. I will describe some important aspects that eROSITA can tackle, and possibly solve, from probing the distributions of hidden massive young stellar clusters to stellar X-ray population synthesis and understanding magnetic dynamos and the evolution of stellar energetic radiation.

Speaker: Jeremy Drake (Smithsonian Astrophysical Observatory)
• 58
X-ray emission from ultracool dwarfs

Ultracool dwarfs (UCDs) are objects with spectral type M7 and later, at the age-dependent transition between stellar and brown dwarf regime. In the predominantly neutral photospheres of UCDs the magnetic field and the matter are expected to show poor coupling, and this should be shutting off the magnetic activity. Nevertheless, radio, Halpha and X-ray emission has occasionally been observed from UCDs.

The most peculiar feature in the multi-wavelength characteristics of UCDs is their radio/X-ray dichotomy: (a) X-ray flaring objects tend to be radio-faint and (b) radio-bursting UCDs are mostly undetected in the X-ray band. These two groups have been associated with (a) `normal' magnetic activity as observed on solar-type stars and (b) phenomena seen on the giant planets of the Solar System, respectively. For UCDs the nature of the corona is thus poorly understood, and they may represent a transition between solar-like and planetary-like magnetic field structure.

I will present several ongoing projects to characterize the multi-wavelength activity of UCDs. These studies include (i) joint XMM-Newton / JVLA observations to examine the dependence of the radio-X-ray relation on other critical parameters such as rotation rate and magnetic field strength, (ii) the serendipitous detection of an X-ray super-flare on an L dwarf, and (iii) a first look into the eFEDS field which comprises a few tens of UCDs and candidate UCDs.

Speaker: Beate Stelzer (IAAT)
• 59
The stellar content of the eROSITA eFEDS field

We have developed a fully Bayesian scheme to statistically
extract the full stellar source content in the eROSITA all-sky survey.
The identification scheme heavily relies on Gaia data, since
all coronal X-ray sources should have a Gaia counterpart with
significant parallax, and assigns to every X-ray source
a probability with which a given X-ray source is stellar. With
our chosen priors the separation between stellar and non-stellar
sources can be performed with quantifiable values for completeness and
reliability. We apply our identification scheme to the eFEDS field, derive the
HR diagram for the stellar eFEDS sources, construct X-ray luminosity
distribution functions and the spatial stratification for the various
stellar types in the Galaxy. The space density of X-ray active giant binary
systems is derived for the first time.

Speaker: Jürgen Schmitt (Hamburger Sternwarte)
• 60
Scanning the Chameleon - The eta Cha cluster seen by eROSITA

The eta Chamaeleontis cluster is a nearby, moderately dispersed star forming region at an intermediate age of 5-10 Myr. Its members are prime targets to study pre-main sequence evolutionary models, accretion properties, disc dispersal and planet formation and are repeatedly observed by major ground and space based facilities. The cluster has been observed by eROSITA in mid November 2019 in the field scan mode. The observed field is centered on the B8V star eta Cha, has an extent of 5x5 deg and an exposure time of 150 ks, corresponding to an exposure depth of about 5 ks.

We present first results from the eROSITA observation of the eta Cha field, that provides sufficient large area coverage and sensitivity to study its members down to stellar masses in the M dwarf regime. Detected sources are cross-matched with Gaia and other datasets to identify and characterize the various stellar populations. For the X-ray brighter sources we perform a spectral and temporal analysis, detail their coronal properties and compare them to previous X-ray measurements.

• 61
Stars in the e-ROSITA eyes

Massive stars of basically all spectral types emit X-rays. Despite tremendous efforts undertaken in the last 20 years, the exact physical mechanisms responsible for their X-ray emission are still not fully understood. The eROSITA survey will deliver a clear X-ray view of massive stars within 2 kpc from the sun. eROSITA's sensitivity in the hard band will become a key diagnostic tool to detect and study massive stars in binaries as well as massive stars with magnetic fields. These stellar properties are of pivotal importance for stellar evolution. Massive stars are the progenitors of neutron stars and black holes. The eROSITA survey strategy is optimally suited to detect X-ray transients, and will deliver much better statistics on massive stars with degenerate companions. This is especially important in the era of gravitational wave astronomy. The results of eRASS will, without doubt, farther motivate population syntheses and detailed studies of evolutionary paths from massive binaries towards double degenerate binaries. In this talk I will briefly review our current knowledge about the X-ray properties of massive star and high-mass X-ray binary populations, and outline what we hope to learn from the results of the eROSITA survey.

Speaker: Dr Lidia Oskinova (Potsdam University)
• 10:55 AM
Coffee Break and Poster viewing
• X-ray view of the Milky Way: SNe and the ISM
• 62
X-ray Studies of Supernova Remnants

Modern X-ray telescopes have revealed the exquisite detail and complexity of supernova remnants (SNRs) at high energies. The metals synthesized in explosions are X-ray bright for many thousands of years, and Chandra, XMM-Newton, Suzaku, and NuSTAR have offered an up-close view of the nucleosynthetic products and their dispersal into the interstellar medium (ISM). In this talk, I will review the major advances facilitated by X-ray observations of SNRs, particularly regarding the nature of explosions, progenitor stars, and particle acceleration. I will also discuss the exciting future prospects for SNR studies, particularly with SRG and X-ray microcalorimeters.

Speaker: Laura Lopez (Ohio State University)
• 63
The Hot Phase of the Interstellar Medium

The interstellar medium (ISM) is heated and ionized by radiation, by stellar winds, and finally, by supernova explosions of massive stars. Since these processes are often correlated in space and time, they can form large interstellar structures called superbubbles, which are filled with hot thin plasma. Supernova remnants and superbubbles can be studied best in soft X-ray line and continuum emission, since the plasma in their interiors is very hot (10^6 − 10^7 K), while non-thermal particles accelerated in the shock waves can also cause X-ray emission. We will present recent results of studies of the hot ISM in the Milky Way and nearby galaxies, in particular in the Magellanic Clouds, and discuss the physics of the hot plasma, the evolution of supernova remnants and superbubbles, and the implications for the star formation history of the galaxies. We will also present first maps of the hot interstellar plasma in the LMC observed with eROSITA.

Speaker: Manami Sasaki (Dr. Karl Remeis Observatory, University of Erlangen-Nurnberg)
• 64
X-ray imaging of the supernova remnants with Spectrum-RG

Supernova remnants are prominent candidates for the acceleration of the Galactic cosmic rays. SNRs are well-known sources of thermal X-ray emission originated from the shock-heated gas and non-thermal (synchrotron) emission caused by very high-energy electrons moving in the magnetic fields. Non-thermal X-ray synchrotron emission provides important information about particle acceleration properties, magnetic field strengths and turbulence near SNR shock fronts. From the observational point of view, SNRs are difficult objects to study in X-ray band due to their large extent on the sky. Thanks to the optimized for X-ray surveys optical design of eRosita and ART-XC telescopes onboard SRG observatory, the X-ray imaging of the extended objects like SNRs is greatly improved in soft (0.3-10 keV, eRosita) and hard (4-30 keV, ART-XC) X-ray bands. First ART-XC performance verification (PV) observation of bright SNR RX J1713.7−3946 and regular slew across SNR Cassiopeia A during the on-going survey, revealed an impressive potential of SRG for studying SNRs. In this talk I will demonstrate imaging capabilities of the ART-XC for extended objects and present first results of observations of the SNRs with ART-XC telescope.

Speaker: Roman Krivonos (Space Research Institute (IKI))
• 65
The SRG/eROSITA view of the W50/SS433

We will present a full-color X-ray view of the radio nebula W50 which harbors the remarkable Galactic microquasar SS 433 provided by SRG/eROSITA. This system is a unique showcase of the impact that sources with hyper Eddington accretion rates might have on their environments, featuring jets, shocks, particle acceleration to Very High Energies and more. An unprecedentedly sensitive and complete X-ray data allow us to identify a number of intricate details highlighting various aspects of the rich multi-component interaction. In future, the presented data will serve as a baseline for combining multiwavelength observations and building a complete physical picture of this "extreme ISM laboratory".

Speaker: Ildar Khabibullin (IKI/MPA)
• 12:55 PM
Lunch Break
• X-ray view of the Milky Way: Compact Objects
• 66
Black Hole X-ray Binaries

Black hole X-ray binaries represent one of the few means available for probing the supernova process, and one of the most useful means for understanding binary evolution under extreme conditions. At the present time, nearly all known black hole X-ray binaries have been selected due to luminous outbursts from their accretion disks. With eROSITA's imaging survey, it will be possible to build up a substantial sample of black holes that have never undergone an outburst, while with its time domain survey, it will become possible to identify some of the faint transient black holes that current all-sky monitors cannot see. I will discuss expected source counts, and means of identification and classification of these objects both from pure X-ray data and from multi-wavelength follow-up.

Speaker: Prof. Thomas Maccarone (Texas Tech University)
• 67
Probing the winds of the most massive stars using high mass X-ray binaries

In high mass X-ray binaries (HMXBs), the black hole or neutron star accretes matter from the wind of a massive supergiant companion: the stellar wind drives changes in the accretion and thus the system’s X-ray emission. But the interaction of this emission with the wind material can also be used to study the wind itself, in particular its geometry, porosity (or clumpiness), mass-loss rate and interaction with the compact object. Such winds are strong and fast and can significantly influence the evolution of massive stars; their observational studies are, however, hampered by a lack of direct diagnostics of the stellar structure. HMXBs are our unique chance to probe these wind structure, in particular through the variable absorption imprinted by the wind onto the continuum emission.

In this talk, I will address some of our recent work on understanding wind accretion in the HMXBs, focusing on different variability timescales. High resolution spectroscopy reveals a complex, multi-phase medium such as would be expected in the case of cold clumps embedded in a hotter wind. X-ray color-color diagrams can be used to assess absorption dips on timescales as short as a few tens seconds even in faint HMXBs; the resulting measure of the stochastic absorption variability constrains the size of the wind clumps. Low cadence observations allow us to constrain the orbital variability of absorption and through it the large-scale accretion geometry onto the compact object and the porosity of wind of the massive stellar companion. I will in particularly highlight how population studies that will be enabled by eROSITA will help us to understand the evolution of the wind properties in HMXBs.

Speaker: Victoria Grinberg (Institut für Astronomie und Astrophysik, Eberhard Karls Universität Tübingen)
• 68
The eROSITA/XMM-Newton PV campaign on PSR B0656$+$14

We report on preliminary results of simultaneous eROSITA and XMM-Newton observations of the isolated neutron star PSR B0656$+$14. Data were obtained for almost 100 ks with eROSITA and 70 ks with XMM-Newton under excellent space weather conditions. The target was chosen to investigate a weak absorption feature between 0.5 and 0.6 keV that was tentatively identified in previous deep XMM-Newton observations, to exploit the improved spectral resolution provided by eROSITA. The pulsar is also used to determine the timing accuracy of the eROSITA cameras in reference to the external XMM-Newton signal. Science opportunities offered by this ultra-deep pointed observation some 8 degrees above the galactic plane are also briefly described.

Speaker: Dr Axel Schwope (AIP)
• 69
Ultra-compact Double Degenerate Binaries

Double degenerate white dwarf binaries result from episodes of common envelope evolution and evolve to short orbital period through gravitational wave emission. When the lighter of the two white dwarfs fills its Roche Lobe, mass transfer is initiated onto the heavier white dwarf, resulting in X-ray emission. At sufficiently close separation, the transferred mass does not form an accretion disk, but rather the ballistic stream impacts the surface of the white dwarf, forming a "direct impact accretor". We will describe an eclipsing double degenerate binary with an orbital period of 6.9 minutes recently discovered by the Zwicky Transient Facility, and discuss the possibility that it exhibits low-level direct impact mass transfer, as well as our attempts to detect X-ray emission from the system. We will also discuss possibilities for detection of direct impact accretors with SRG.

Speaker: Thomas Prince (Calech)
• 70
Study of transient sources with SRG/ART-XC

During first months of the SRG operation the ART-XC telescope (working energy range 4-30 keV) performed observations in different modes: scanning observations of a number of sky fields, pointing observations and all-sky survey. These observations allowed us to discover new transient sources with different observational properties. In particular, the typical time variability of new sources is spanned from dozens seconds or several hours (e.g., for SRGt J123822.3-253206) up to several days (e.g., for SRGa J174956-34086). Spectral characteristics of new sources are also significantly different, that point out to their different nature. In addition to new sources a number of known transient ones in our and nearby galaxies were studied as well. In this presentation we report above mentioned results as well as briefly present the system for the quick look analysis of the ART-XC data.

Speaker: Alexander Lutovinov (Space Research Institute (IKI))
• 4:05 PM
Coffee Break and Posters viewing
• 71
Binary X-ray source populations at different accretion stages

We employ a binary population synthesis, combined with a detailed treatment of mass transfer onto neutron stars and black holes from the optical component with the help of the MESA stellar evolution code, to model populations of binary X-ray sources in galaxies. Wind-fed accreting neutron stars are calculated with taking into account different regimes of quasi-spherical accretion onto magnetised neutron stars (Bondi-Hoyle or settling subsonic, depending on the plasma cooling near the neutron star magnetosphere). Features of the supercritical disk accretion onto black holes and magnetised neutron stars are also taken into account. Our model enables us to reproduce the observed properties of specific X-ray binary types, including symbiotic X-ray binaries, Be-X-ray binaries and ultraluminous X-ray sources. We also model the X-ray luminosity function from different X-ray binary populations in galaxies with an account of the star formation rate history and metallicity evolution. The X-ray luminosity function can be used as a tool to study properties of X-ray binary populations observed in X-ray sky surveys.

Speaker: Prof. Konstantin Postnov (Sternberg Astronomical Institute)
• 72
The ART-XC Galactic Bulge Survey

In August-September 2019, the ART-XC telescope scanned a large field (about 40 sq. deg) around the Galactic Center for nearly 3 weeks as part of the SRG Cal-PV phase. This resulted in a unique survey of the Galactic Bulge in the hard X-ray band of 4-30 keV. The main results of this survey will be presented, with a focus on the statistical properties of cataclysmic variables and low-luminosity X-ray binaries.

Speaker: Prof. Sergey Sazonov (Space Research Institute, Moscow)
• 73
The SRG/ART-XC survey of the Galactic Plane fields in the direction to the Norma arm and l=+20

We present results of the survey of two regions of the Galactic Plane (Norma
arm and the region around galactic longitude l=+20 deg), obtained with the ART-XC telescope
on board the SRG observatory in hard X-rays during the Cal-PV phase. The
total area covered by this survey was about 50 sq.degrees with the median
exposures of ~700 s in the l+20 field and ~1.4 ks in the Norma arm field, respectively,
that led to the detection of several dozens sources of a different nature.
The properties of this sample as well as individual properties of several bright
sources are discussed.

Speaker: Dr Andrey Semena (IKI RAS)
• 74
First results of the SRG/eROSITA Galactic Plane survey at l=20

We will present the first results of a deep raster-scan
observation of the Galactic plane field, carried out by the
SRG/eROSITA telescope as a part of its CalPV program.
The field is centered at Galactic longitude l=20 degrees and covers a
total area of 25 sq. deg with a mean exposure of 8 ksec. We have
detected more than 2000 individual point X-ray sources,
demonstrating a wide variety of spectral properties, many of them having
counetrparts in GAIA and other optical catalogs. We will
present the log N(>S) - log S distributions of detected sources, their spectral
properties and discuss the overall picture of the Galactic X-ray source population.

Speaker: Mr Pavel Medvedev (Space Research Institute (IKI), Moscow)
• 75
Low level accretion activity in X-ray binaries

Low-mass X-ray binaries can lay dormant, remaining undetected for decades, until they are usually detected by X-ray monitoring satellites when they undergo bright outbursts. However, during these periods of quiescence between outbursts, low level accretion does occur but usually cannot be studied at X-ray energies due to their extremely low fluxes. We have been monitoring ~40-50 X-ray binaries with the Faulkes Telescopes / Las Cumbres Observatory (LCO) global robotic network for more than a decade. We find evidence for low level, variable accretion activity, long-term trends and jets being launched at 10^-6 - 10^-8 times the Eddington luminosity in some systems. Different activity states exist in quiescence. The X-ray spectra of quiescent X-ray binaries are described by a power law; different sources have slightly different spectra. eROSITA on SRG will achieve high S/N soft X-ray spectra of Galactic quiescent low-mass X-ray binaries. We wish to test if accretion activity (identified by our optical monitoring) correlates with the X-ray properties uncovered by eROSITA. I will also introduce our new real-time optical monitoring pipeline, the "X-ray Binary New Early Warning System (XB-NEWS)", which aims to detect and announce new X-ray binary outbursts within a day of first optical detection. We are now detecting the early stages of these outbursts with our optical telescopes, before they become bright enough for X-ray detection. This allows us to trigger X-ray and multi-wavelength campaigns during the very early stages of outbursts, to constrain the outburst triggering mechanism.

Speaker: David Russell (New York University Abu Dhabi)
• Friday, March 20
• Time domain and multi-messenger astronomy
• 76
The transient X-ray sky

The eROSITA instrument onboard the SRG satellite provides a unique opportunity
for discovering transients in its X-ray All Sky survey data. There are many
classes of transients known to emit in X-rays, ranging from flares from active
stars to fast blazar variability. By necessity, I will highlight a few such
source classes and the open science questions that will benefit tremdously from
the eROSITA All Sky Survey and timely follow-up. In particular, I will focus on
tidal disruption events and the source class of fast X-ray transients.

Speaker: Prof. Peter Jonker (Radboud University & SRON, Netherlands Institute for Space Research)
• 77
Infant Supernova Explosions: the ZTF/SRG Synergy

The study of massive stars exploding as supernovae has seen a major breakthrough in recent years, with modern surveys making the detection and exploration of supernova explosions within a day of stellar core collapse possible. With its extremely wide field of view and mature infrastructure of integrated hardware, software and operations, the Zwicky Transient Facility (ZTF) has made such detections a matter of routine. The first hours and days of cosmic explosions reveal a plethora of new physics: from the physics of the energetic shock breakout flares, via measurement of the explosion energy and extending to extensive mapping of the exploding star parameters: its radius, surface composition, and evolutionary history. X-ray emission is predicted (and was observed in a single serendipitous case) from the brief shock breakout phase, and more extended emission may result from interaction of the SN ejecta with circumstellar material that we have shown often surrounds the exploding massive progenitors. The ability to survey wide sky areas rapidly and synchronously from ground (visible) and space (X-ray) promises very high scientific returns.

Speaker: Prof. Avishay Gal-Yam (Weizmann Institute of Science)
• 78
Tidal Disruption Events

X-ray observations of Tidal Disruptions Events (TDEs) are a unique probe of the physics of accretion around supermassive black holes, as they are thought to transition from super- to sub-Eddington accretion on timescales of months/years. The first TDE candidates were found in the X-rays with the ROSAT All-Sky Survey, but, today, most of our candidates are found in the optical. While optical surveys have increased our numbers of TDE candidates enormously, it remains unclear where the optical emission originates, and if X-ray TDEs are part of the same population. Discovering TDEs in X-rays is key to understanding the emission mechanisms and rates of TDEs where the stellar debris is efficiently accreting on to the black hole. In this talk I will discuss the current state of the field, and what questions astronomers hope that eROSITA will resolve.

Speaker: Erin Kara (MIT)
• 79
Tidal Disruption Events in the eROSITA Era

Due to eROSITA’s cadence and its 30-fold increased sensitivity in the soft X-ray band relative to ROSAT, eROSITA promises to detect 1000s of tidal disruption event (TDE) candidates during its all sky survey phase. I will present our machine-learning assisted approach for identifying TDE candidates amongst the millions of X-ray sources in eROSITA's source catalogues, and selected early results from the first months of the all-sky survey.

• 80
The Changing-Look Zoo

Almost 200 changing-look AGN/quasars are currently known showing significant spectroscopic and photometric variability on timescales of months to years. Although initially discovered by serendipity, systematic searches of archival survey data, such as SDSS, Pan-STARRS, and CRTS, have identified such sources in significant numbers. Ongoing time domain sky surveys, such as ZTF, which cover the visible sky every few nights, are enabling real-time monitoring of such objects as they transition between different states of activity. However, the known set of changing-look sources spans a range of luminosity, black hole mass, and Eddington ratio and this suggests that a number of different physical mechanisms may be contributing to the same broad observed phenomenology. X-ray observations may well be the key to distinguishing between different models, particularly if contemporaneous with optical observations. In this talk, I will review the current state of the field, and consider how a joint ZTF-SRG data set will greatly improve our understanding of this phenomenon.

Speaker: Prof. Matthew Graham (Caltech)
• 81
eROSITA constraints on the AGN duty cycle

During its PV phase eROSITA observed a ~100 deg2 field to the final depth expected after eight all-sky scans. The XMM Atlas survey is covered in this field. Between these data sets, we search for dramatic flux changes in AGN which would indicate AGN ignition/shut-down. I will present a few candidate events. We will extend this work using the data of all individual eight all-sky surveys by eROSITA. The number of expected events and the clean selection of sources allows us to compute the probabilities that such changes happen. This will result in observational constraints on the AGN duty cycle. For selected events we will trigger follow-up observations (e.g., XMM, VLT).

Speaker: Dr Mirko Krumpe (AIP)
• 11:00 AM
Coffee Break
• 82
TBD
Speaker: Marek Kowalski (DESY and Humboldt University Berlin)
• 83
Treasures from the Zwicky Transient Facility Galactic Plane observations and its connection to eROSITA

The Zwicky Transient Facility (ZTF) started science operation in March 2018. 40% of ZTF observing time is dedicated to two public surveys: one covering the entire Northern sky every three nights in g and r passbands and one visiting the Galactic Plane every night in g and r. In addition to the public Galactic Plane survey, ZTF has conducted a dedicated high-cadence survey of selected Galactic Plane fields to study the ultra-short variable sky. So far we have covered about 4900 sqd. In this talk, I will present an overview of the ZTF Galactic Plane observations and present some science highlights from the first two years, including several new accreting binaries which are ideal for multi-wavelength studies with eROSITA. This includes the discovery of a new class of helium stars in accreting ultracompact binaries which are potential progenitors for Type Ia supernovae.

Speaker: Dr Thomas Kupfer (KITP)
• 84
Transient ULXs and prospects for SRG

Ultraluminous X-ray sources are powerful extra-nuclear sources of X-rays found in nearby galaxies, which in most cases are believed to be powered by super-Eddington accretion onto neutron stars and black holes. While most known ULXs are persistent sources, recently some new sources have been found that appear to come and go. I will present results from a systematic search for these transient ULXs in Swift/XRT data, what they might tell us about super-Eddington accretion, and discuss the prospects for SRG surveys.

Speaker: Dr Brightman Murray (Caltech)
• 85
XMM-Newton Joint Observing Programs and TOOs: Potential for Synergies with eROSITA

XMM-Newton supports currently nine joint programs and observes about 30% of its high priority targets simultaneously with other facilities. In addition, the observing program shows and exceptional high amount of TOO observations in comparison to other large observatory class mission. The talk describes the policy for joint programs and TOO and reflects on the potential for synergies with eROSITA.

Speaker: Norbert Schartel (ESA)
• 86
Synergies between XRISM and SRG/eROSITA
Speaker: Matteo Guainazzi (ESA)