GeV–TeV Counterparts of SS 433/W50 from Fermi-LAT and HAWC Observations

Abstract

The extended jets of the microquasar SS 433 have been observed in optical, radio, X-ray, and recently very-high-energy γ -rays by High Altitude Water Cerenkov (HAWC). The detection of HAWC γ -rays with energies as great as 25 TeV motivates searches for high-energy γ -ray counterparts in the Fermi -Large Area Telescope (LAT) data in the 100 MeV–300 GeV band. In this paper, we report on the first joint analysis of Fermi -LAT and HAWC observations to study the spectrum and location of γ -ray emission from SS 433. Our analysis finds common emission sites of GeV-to-TeV γ -rays inside the eastern and western lobes of SS 433. The total flux above 1 GeV is in both lobes. The γ -ray spectrum in the eastern lobe is consistent with inverse Compton emission by an electron population that is accelerated by jets. To explain both the GeV and TeV flux, the electrons need to have a soft intrinsic energy spectrum, or undergo a quick cooling process due to synchrotron radiation in a magnetized environment.