Fermi Gamma-ray Space Telescope

The puzzling case of HESS J1640-465 and HESS J1641-463 as seen by the Fermi-LAT

Helene Laffon
Marianne Lemoine-Goumard, Marie-Helene Grondin, Thierry Reposeur, Fabio Acero, Helene Laffon on behalf of the Fermi-LAT collaboration

Abstract:

Thanks to a longer dataset and improved sensitivity afforded by the P7 reprocessed data of the Fermi Large Area Telescope, the TeV source HESS J1641-463 is now detected by the Fermi-LAT. This new detection implies a change in the GeV spectrum of the neighboring bright source associated to HESS J1640-465 which was previously contaminated by the Fermi source associated with HESS J1641-463. The newly obtained GeV spectrum associated with HESS J1640-465 is harder and links up naturally with the spectral points obtained by H.E.S.S., suggesting a hadronic origin. However, this is not the case for the overall spectral energy distribution of HESS J1641-463 whose origin remains enigmatic. A detailed analysis of this region with the Fermi-LAT will be presented as well as different scenarios to explain the gamma-ray emission observed from these two sources.