The Spectral Parameters of Gamma-Ray Blazars

Abstract

The blazars are the brightest astrophysical objects in the extragalactic gamma-ray sky and divided into two main classes, Flat Spectrum Radio Quasars (FSRQs) and BL Lac objects (BLs). Blazars emit radiation via non-thermal processes including synchrotron and inverse Compton (IC), and their multiband spectra are peaked and highly curved. We find that FSRQs show higher curvature than BLs, that might be due to complex radiation mechanisms. We investigate the relationship between spectral parameters of BLs to investigate the signatures of particle acceleration and cooling in plasma jets of blazars. The synchrotron peak frequency of BLs is correlated with the spectral curvature, that is a signature of stochastic particle acceleration. The synchrotron peak frequency also shows an inverse correlation with gamma-ray luminosity and the Compton dominance, that is a signature of blazar sequence. We, therefore, suggest that the synchrotron peak frequency in BLs is dominated by radiative cooling and arises due to a cooling break, whereas the curvature might arise due to a stochastic particle acceleration mechanism.