On the Spectral Break in the Fermi-LAT Spectrum of 3C 454.3

TL;DR

This paper explains the sharp spectral break observed in 3C 454.3's gamma-ray spectrum using a two-component model involving disk and broad-line region radiation, challenging previous synchrotron self-Compton explanations.

Contribution

It introduces a model combining Compton-scattered disk and BLR radiation to account for the spectral break, consistent with a wind-like BLR density profile.

Findings

Spectral break at ~2.4 GeV with ΔΓ ≈ 1.2

Two-component model fits multiwavelength data well

BLR density gradient explains the sharp break

Abstract

Fermi Gamma ray Space Telescope observations of the flat spectrum radio quasar 3C~454.3 show a spectral-index change $\Delta \Gamma \cong 1.2\pm 0.3$ at break energy $E_{br} \approx 2.4\pm0.3$ GeV. Such a sharp break is inconsistent with a cooling electron distribution and is poorly fit with a synchrotron self-Compton model. We show that a combination of two components, namely the Compton-scattered disk and broad-line region (BLR) radiations, explains this spectral break and gives a good fit to the quasi-simultaneous radio, optical/UV, X-ray, and $\gamma$-ray spectral energy distribution observed in 2008 August. A sharp break can be produced independent of the emitting region's distance from the central black hole if the BLR has a gradient in density $\propto R^{-2}$, consistent with a wind model for the BLR.