2017MNRAS.470.3283S

We perform a detailed spectral study of a recent flaring activity from the flat spectrum radio quasar (FSRQ), 3C 454.3, observed simultaneously in optical, UV, X-ray and γ-ray energies during 2015 August 16-28. The source reached its peak γ-ray flux of (1.9 ± 0.2) x 10^–05 ph cm^–2 s^–1 on August 22. The time-averaged broad-band spectral energy distribution (SED) is obtained for three time periods, namely 'flaring state', covering the peak γ-ray flux; 'post-flaring state', immediately following the peak flare and 'quiescent state', separated from the flaring event and following the post-flaring state. The SED corresponding to the flaring state is investigated using different emission models involving synchrotron, synchrotron self-Compton (SSC) and external Compton (EC) mechanisms. Our study suggests that the X-ray and γ-ray emission from 3C 454.3 cannot be attributed to a single emission mechanism and instead, one needs to consider both SSC and EC mechanisms. Moreover, the target photon energy responsible for the EC process corresponds to an equivalent temperature of 564 K, suggesting that the flare location lies beyond the broad line emitting region of the FSRQ. The SED fitting of the other two flux states further supports these inferences.