Speaker
Dr
Gudlaugur Johannesson
(Science Institute, University of Iceland)
Description
The high energy diffuse emission originates when cosmic-rays (CRs) interact with the
interstellar medium (ISM) and interstellar radiation field (ISRF). It is the dominant
source of gamma-rays in the Fermi-LAT data, accounting for more than half of the
photons. Observations of the diffuse emission can be used to explore CR origin and
propagation in the Milky Way when combined with modeling of the diffuse emission. We
utilize the GALPROP code to create a grid of models by varying within observational
limits the size of the propagation halo, the CR source distribution and the
interstellar gas distribution. The models are compared to 21 months of Fermi-LAT data
using an all sky maximum likelihood fit where we determine the radial distribution of
the X_CO factor, a normalization factor for the ISRF, the spectral shape of the
sources from the first Fermi-LAT catalog, and the spectral shape of the isotropic
background, all of which have some dependence on the assumed diffuse emission model.
The models are compared on their maximum likelihood ratio, as well as spectra,
longitude and latitude profiles, and residual maps.
Primary author
Dr
Gudlaugur Johannesson
(Science Institute, University of Iceland)
