# Clues on High Energy Emission Mechanism from Blazar 3C 454.3 during 2015 August Flare

## TL;DR

This study analyzes the multi-wavelength spectral data of blazar 3C 454.3 during its 2015 flare, revealing that both SSC and EC mechanisms contribute to high-energy emissions and locating the emission region beyond the broad line region.

## Contribution

It provides a detailed spectral analysis of the 2015 flare, demonstrating the necessity of combining SSC and EC models to explain the high-energy emission mechanisms.

## Key findings

- Both SSC and EC mechanisms are needed to explain X-ray and gamma-ray emissions.
- The EC target photon temperature indicates emission occurs beyond the broad line region.
- SED modeling supports the multi-mechanism emission scenario.

## Abstract

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 $\gamma$-ray energies during 16 to 28 August, 2015. The source reached its peak $\gamma$-ray flux of $(1.9\pm0.2)\times\,10^{-05} \; {\rm ph\,cm^{-2}\,s^{-1}}$ on 22 August. The time averaged broadband spectral energy distribution (SED) is obtained for three time periods, namely "flaring state"; covering the peak $\gamma$-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 $\gamma$-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. SED fitting of the other two flux states further supports these inferences.