2018RAA....18....6Z

We investigate the γ-ray and X-ray properties of the flat spectrum radio quasar (FSRQ) 4C 50.11 at redshift z = 1.517. The Fermi-LAT data indicate that this source was in an active state since July 2013. During this active period, the source's emission appeared harder in γ-rays, with the flux having increased by more than a factor of three. We analyze two distinct flares seen in the active state and find that the variability is as short as several hours. The Swift-XRT data show that the source was variable at X-ray energies, but no evidence is found for flux or spectral changes related to the γ-ray activity. The broad-band X-ray spectrum obtained with Swift-XRT and NuSTAR is described well by a broken power law model, with an extremely flat spectrum (Γ₁ ∼ 0.1) below the break energy, E_break ∼ 2.1 keV, and Γ₂ ∼ 1.5 above the break energy. The spectral flattening below ∼ 3 keV is likely due to the low energy cut-off in the energy distribution of the photon-emitting electron population. We fit the broad-band spectral energy distribution of the source during both the active and quiescent states. The X-ray and γ-ray emission from the jet is mainly due to the inverse-Compton scattering process, with seed photons provided from the broad line region, and the jet is estimated to be larger than the accretion power if the jet is mainly composed of electron-proton pairs.