A spectral hardening in the Fermi-LAT Data of 1ES 0502+675

Abstract

The 𝛾-ray spectral feature of the blazar 1ES 0502+675 is investigated by using Fermi Large Area Telescope (Fermi-LAT) Pass 8 data (between 100 MeV and 300 GeV) covering from 2008 August to 2021 April. A significant (∼ 4𝜎) hardening at ∼ 1 GeV is found in the 𝛾-ray spectrum during a moderately flaring state (MJD 55050-55350). The photon index below and above the break energy is Γ 1 = 2.36 ± 0.31 and Γ 2 = 1.33 ± 0.11, respectively. In the rest of the observations, the 𝛾-ray spectrum can be described by a power-law form with the photon index of ≈ 1.6. In the frame of a one-zone synchrotron self-Compton (SSC) model, the spectral hardening is interpreted as the transition between the synchrotron component and the SSC component. This could be the result of a slight increase of the break/maximum Lorentz factor of the electrons.