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