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