Speaker
Dr
Timur Delahaye
(Madrid UAM/CSIC)
Description
The Galactic gamma-ray diffuse emission is currently observed in the GeV-TeV energy range with
unprecedented accuracy by the
Fermi satellite. Understanding this component is crucial as it provides a background to many different signals
such as extragalactic
sources or annihilating dark matter. It is timely to reinvestigate how it is calculated and to assess the various
uncertainties which are
likely to affect the accuracy of the predictions. The Galactic gamma-ray diffuse emission is mostly produced
above a few GeV by the
interactions of cosmic ray primaries impinging on the interstellar material. The theoretical error on that
component is derived by
exploring various potential sources of uncertainty. Particular attention is paid to cosmic ray propagation.
Nuclear cross sections, the
proton and helium fluxes at the Earth, the Galactic radial profile of supernova remnants and the hydrogen
distribution can also
severely affect the signal. The propagation of cosmic ray species throughout the Galaxy is described in the
framework of a semi-
analytic two-zone diffusion/convection model. This allows to convert the constraints set by the boron-to-carbon
data into a theoretical
uncertainty on the diffuse emission. New deconvolutions of the HI and CO sky maps are also used to get the
hydrogen distribution
within the Galaxy. The thickness of the cosmic ray diffusive halo is found to have a significant effect on the
Galactic gamma-ray
diffuse emission while the interplay between diffusion and convection has little influence on the signal. The
uncertainties related to
nuclear cross sections and to the primary cosmic ray fluxes at the Earth are significant. The radial distribution
of supernova remnants
along the Galactic plane turns out to be a key ingredient. As expected, the predictions are extremely sensitive
to the spatial
distribution of hydrogen within the Milky Way.
Primary author
Dr
Timur Delahaye
(Madrid UAM/CSIC)
Co-authors
Dr
Armand Fiasson
(LAPP Annecy)
Prof.
Martin Pohl
(DESY Hamburg)
Prof.
Pierre Salati
(LAPTh Annecy)
