On the origin of GeV spectral break for Fermi blazars: 3C 454.3

Abstract

The GeV break in spectra of the blazar 3C 454.3 is a special observation feature that has been discovered by the Fermi-LAT. The origin of the GeV break in the spectra is still under debate. In order to explore the possible source of GeV spectral break in 3C 454.3, a one-zone homogeneous leptonic jet model, as well as the McFit technique are utilized for fitting the quasi-simultaneous multi-waveband spectral energy distribution (SED) of 3C 454.3. The outside border of the broad-line region (BLR) and inner dust torus are chosen to contribute radiation in the model as external, seed photons to the external-Compton process, considering the observed -ray radiation. The combination of two components, namely the Compton-scattered BLR and dust torus radiation, assuming a broken power-law distribution of emitted particles, provides a proper fitting to the multi-waveband SED of 3C 454.3 detected 2008 Aug 3 -Sept 2 and explains the GeV spectral break. We propose that the spectral break of 3C 454.3 may originate from an inherent break in the energy distribution of the emitted particles and the Klein-Nishina effect. A comparison is performed between the energy density of the 'external' photon field for the whole BLR BLR achieved via model fitting and that constrained from the BLR data. The distance from the position of the -ray radiation area of 3C 454.3 to the central black hole could be constrained at ∼ 0.78pc (∼ 4.00 BLR , the size of the BLR).

Modeling the Broadband Emission of 3C 454.3

“…The EC disk component dominates in the sub-GeV band, while the contribution of EC BLR is significant at HEs. However, the 𝛾-ray data can be explained also when considering the joint inverse Compton scattering of BLR and torus photons (e.g., see Kang et al 2021).…”