On the gamma-ray emission from 3C 120

We report the analysis of Fermi Large Area Telescope data from five years of observations of the broad line radio galaxy 3C 120. The accumulation of larger data set results in the detection of high-energy $γ$-rays up to 10 GeV, with a detection significance of about $8.7σ$. A power-law spectrum with a photon index of $2.72\pm0.1$ and integrated flux of $F_γ=(2.35\pm0.5)\times10^{-8}\:\mathrm{photon\:cm}^{-2}s^{-1}$ above 100 MeV well describe the data averaged over five year observations. The variability analysis of the light curve with 180-, and 365- day bins reveals flux increase (nearly twice from its average level) during the last year of observation. This variability on month timescales indicates the compactness of the emitting region. The $γ$-ray spectrum can be described as synchrotron self-Compton (SSC) emission from the electron population producing the radio-to-X-ray emission in the jet. The required electron energy density exceeds the one of magnetic field only by a factor of 2 meaning no significant deviation from equipartition.

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