Fermi LAT Observation of Supernova Remnant HB9

Abstract: A 5.5-year Fermi LAT gamma-ray observation shows significant extended emission at the position of the supernova remnant HB9 (G160.9+2.6). The significance of the detection above the background for photon energies above 0.2 GeV is 16$\sigma$. The gamma-ray flux above 0.2 GeV is (2.23E-8) photons/cm$^2$ s, and the corresponding luminosity above 1 GeV is 1.4E33 erg/s (for a source distance of 1 kpc). The spectrum of the source is best described by a curved power-law (log-parabola). The gamma-ray spectrum of the source is consistent with both leptonic and hadronic models, and the relevant physical parameters in each case are derived. More studies on the ambient density in the region of HB9 should be carried out to rule out or confirm hadronic and non-thermal bremsstrahlung scenarios for the gamma-ray emission.