High-Energy γ -Ray Emission from PKS 0625-35

Abstract

We present the γ -ray observations of the radio galaxy PKS 0625-35, using the Fermi Large Area Telescope data accumulated during 2008-2017. γ -rays up to 100 GeV have been detected with a detection significance of about 32.3σ . A power law spectrum with a photon index of 1.88±0.04 and an integrated flux of Fγ = (1.02 ± 0.10)×10-8 photon cm-2 s-1 above 100 MeV well describes the data averaged over 9 years of observations. There is a hint of deviation from a simple power-law shape around tens of GeV energies; however, the low statistics does not allow one to reject power law modeling. The spectral energy distributions during high and low X-ray states are modeled using one-zone leptonic models that include the synchrotron, synchrotron self Compton processes; the model parameters are estimated using the Markov Chain Monte Carlo method. The modeling shows that in the jet of PKS 0625-35 the particles (electrons) are accelerated to energies higher than 50 TeV.