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 (VHE) γ-rays by 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-LAT data in the 100 MeV-300 GeV band. In this paper, we report on the first-ever 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 ∼ 1 × 10 −10 cm −2 s −1 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.

Physical properties of the molecular cloud, N4, in SS433; Evidence for an interaction of molecular cloud with the jet from SS433

“…This may indicate the magnetic field is weak or the radio continuum emission tracing the magnetic field already disappeared by synchrotron radiation. The GeV gamma-ray emission has recently been detected toward the jet from SS433 (Abeysekara et al 2018;Fang et al 2020;. N4 is located at the edge of the distribution of the gamma-ray emission.…”

“…There gamma-ray radiation up to TeV was detected, and the origin of the TeV gamma-ray was discussed to result from the interaction of high energy cosmic-ray proton with an interstellar proton. Various gamma-ray observations have been conducted toward the SS433/W50 system (e.g., Abeysekara et al 2018;Fang et al 2020). Actually, toward the jet from SS433, Gev-TeV gamma-ray have been detected, and their origins have been discussed…”

“…The dense ISM in and around the SS433/W50 system can be a site of the gamma-ray radiation induced by an interaction of a high energy cosmic-ray proton accelerated through diffusive shock acceleration (Fermi 1949) with a hydrogen atom (hadronic process). High energy gamma-ray radiation at a few hundred GeV to 100 TeV has been detected by Fermi-LAT, HAWC (High Altitude Water Cherenkov Observatory) (Abeysekara et al 2018;Fang et al 2020). The origin of such GeV-TeV gamma-ray radiation is considered to be inverse Compton scattering.…”

Multi-messenger Implications of Sub-PeV Diffuse Galactic Gamma-Ray Emission

“…Assuming that Q e ∝ E −2 e up to a maximum energy E e,max = 3 PeV and source emission time ∼ 0.1 Myr (just for demonstrative purposes), we find that the total electron power L e = Ee,max mec 2 ∼ 10 37 (d/5 kpc) 2 erg s −1 is sufficient to explain the Tibet ASγ flux, where d is the average source distance. Although the mechanism of PeV electron acceleration remains an open question, leptonic sources with such hard spectra and high E e,max have been previously observed (see, e.g., HAWC Collaboration et al 2018Collaboration et al , 2019Fang et al 2020).…”

Deciphering the Origin of the GeV--TeV Gamma-ray Emission from SS 433

“…Recently, Fang et al (2020) performed a joint analysis of LAT and HAWC data, and concluded that the GeV gamma-ray data may be smoothly connected to the TeV range with a photon index Γ ∼ 2.1. They found that the previous LAT analyses were affected by nearby sources, J1913.3+0515 in the LAT 8-year point source catalog and J1907.9 + 0602 in the 4FGL catalog (The Fermi-LAT collaboration 2019).…”