Composition of the Fermi-LAT IGRB and constraints on the galactic Dark Matter
by
Mattia Di Mauro(University of Turin)
→
Europe/Berlin
Building 67, SemRm 10 (DESY Hamburg)
Building 67, SemRm 10
DESY Hamburg
Description
I present a model of diffuse gamma-ray emission from AGN and Pulsars which together with other gamma-ray emission mechanisms could fully explain the IGRB Fermi-LAT data and sets sever constraints on thermally produced WIMP as Dark Matter candidate. The nature of the Isotropic gamma-ray Background (IGRB) measured by the Large Area Telescope (LAT) on the Fermi gamma-ray space Telescope (Fermi) is one of the most intriguing mystery in astrophysics. We have derived the diffuse gamma-ray emission from unresolved Active Galactic Nuclei (AGN) with a large viewing angle with respect to the line-of-sight (MAGN). Our results demonstrate that the MAGN can contribute from 10% up to nearly the entire measured IGRB. We evaluate a theoretical uncertainty on the flux of almost an order of magnitude.
We have also calculated the gamma-ray flux from unresolved BL Lacertae, a class of AGN with the jet emission aligned with the line of sight. The diffuse emission from these objects grows from about 10$%$ of the measured IGRB at 100 MeV to ~100% of the data level at 100 GeV. At energies greater than 100 GeV, our predictions naturally explain the IGRB data, accommodating their softening with increasing energy. Uncertainties are estimated to be within of a factor of two of the best fit flux up to 500 GeV.
We have performed also a detailed analysis on Pulsars, the most abundant galactic gamma-ray source population. We have derived the diffuse gamma-ray emission from both young and old (Millisecond) Pulsars showing that this source population gives a negligible contribution to the IGRB. We have also demonstrated that MAGN and BL Lacertae sources together with Flat Spectrum Radio Quasar, Pulsar and Star Forming Galaxy populations could fully explain the spectra of IGRB intensity in the entire energy range (200 MeV-800 GeV).
A more exotic contribution to the IGRB invokes the pair annihilation of dark matter (DM) weakly interacting massive particles (WIMPs) into gamma-rays. We have taken into account the diffuse gamma-ray emission from the above cited source populations to evaluate the room left for galactic DM at high latitudes by including photons from both prompt emission and inverse Compton scattering. We demonstrate that the IGRB has the potential to be one of the most competitive way to test the DM WIMP hypothesis.
