2019PASP..131a4101Y

We analyze 10 years of Fermi γ-ray observations of the high-redshift blazar S5 0836+71 (z = 2.172) that showed a strong flare in 2015 characterized by a several-fold increase in the γ-ray flux within a few days. The discrete correlation function between the γ-ray and the R band (AZT-8) shows a highly significant (>99.9% confidence) correlation with the γ-ray variations leading the R band by about 75 days. The spectral energy distributions are modeled, with the adoption of a synchrotron self-Compton plus external Compton (EC) model, to discuss the reasons of transition between the low- and high-flux states. In both the pre-flare and flare states, the EC seed photons might be dominated by reprocessed emission from the dusty torus rather than the broadline region (BLR). This implies the location of radiating blob outside the BLR and inside the dusty torus. From the pre-flare state to the flare state, δ and B decrease, whereas N₀ and γ_max increase accordingly. The results of the modeling suggest that the increase in the total number of emitting electrons and hardening of the power spectrum of emitting electrons are primary causes of the flare in γ-rays.