Tentative evidence of spatially extended GeV emission from SS433/W50

Abstract

We have analyzed ten years of the Fermi Large Area Telescope data toward the SS433/W50 region. With the latest source catalog and diffuse background models, the γ-ray excess from SS433/W50 is detected with a significance of ~6σ in the photon energy range of 500 MeV-10 GeV. Our analysis indicates that an extended flat disk morphology is preferred over a point-source description, suggesting that the GeV emission region is much larger than that of the TeV emission detected by the High Altitude Water Cherenkov (HAWC) telescope. The size of the GeV emission is instead consistent with the extent of the radio nebula W50, a supernova remnant being distorted by the jets, so we suggest that the GeV emission may originate from this supernova remnant. The spectral result of the GeV emission is also consistent with a supernova remnant origin. Furthermore, we derive the GeV flux upper limits on the TeV emission region, which put moderate constraints on the leptonic models to explain the multiwavelength data.