Revision of the GeV γ-Ray Emission in the Region of HESS J1813-178 with Fermi-LAT

Abstract

HESS J1813-178 is one of the brightest and most compact TeV γ -ray sources, and whether its γ -ray emission is associated with supernova remnant (SNR), pulsar wind nebula (PWN), or young stellar cluster (YSC) is still under debate. By analyzing the GeV γ -ray data in the field of HESS J1813-178 using 14 yr of PASS 8 data recorded by the Fermi Large Area Telescope (Fermi-LAT), we report the discovery of three different sources with different spectra in this region. The hard source with a PL spectral index of 2.11 ± 0.08 has a small size extension, which is spatially and spectrally coincident with the TeV γ -ray emission from HESS J1813-178. CO observations display the dense molecular clouds surrounding HESS J1813-178 in the velocity range of 45–60 km s ^−1 . The possible origins of the γ -ray emission from HESS J1813-178 are discussed, including SNR G12.820.02, the PWN driven by the energetic X-ray pulsar PSR J1813-1749 and YSC Cl 1813-178. However, none of them can be ruled out clearly. Note that the maximum energy of protons in the hadronic model should exceed a few hundred TeV, which makes HESS J1813-178 a promising PeVatron. A detailed LHAASO data analysis about the morphology and spectrum would be helpful to investigate the origin of the γ -ray emission in this region and test its PeVatron nature.

Keywords

• Gamma-ray sources
• Supernova remnants
• Pulsar wind nebulae
• Star clusters
• Molecular clouds