Poster Abstract
We study the evolution of spectral curvature of emitting electron energy distribution (EED) against its peak energy in a combined stochastic acceleration and cooling scenario by inverse Compton (IC) modeling of spectral energy distributions (SEDs) of Fermi bright blazars. The blazar sample shows the theoretical blazar sequence between jet power and peak energy, and another sequence between jet power and curvature, suggesting that spectral curvature might be an important parameter of blazar sequence. Curvature evolves differently in blazars depending on the source conditions. We find that the curvature anti-correlates with peak energy in BL Lac objects (BL Lacs), that is a signature of pure hard-sphere stochastic acceleration. The curvature of FSRQs rather evolves in a transition cooling regime, where curvature either correlates positively with the peak energy or remains steady.
Plain text summary
The blazars are bright extragalactic sources powered by accretion on to a supermassive black hole. Blazars are broadband emitters of nonthermal radiation and their spectra significantly deviate from a power-law. The broadband spectral energy distribution (SED) of a blazar is significantly curved. The curvature of SED must related to an intrinsic curvature of source electron energy distribution (EED). We study the evolution of spectral curvature against peak energy in a combined cooling and stochastic acceleration scenario by inverse Compton (IC) modeling the simultaneous broadband SEDs of Fermi bright blazars. We find that the curvature decreases from FSRQs toward high synchrotron peak BL Lac objects, that may be related to different physical conditions in the jet. The blazar sample shows an anti-correlated sequence between jet power and electron peak energy and a positively correlated sequence between jet power and curvature, suggesting that the curvature might be an important parameter of blazar sequence. We find that the curvature anti-correlates with peak energy in BL Lac objects, that is a signature of pure hard-sphere type stochastic acceleration. The curvature in BL Lac objects evolves in the acceleration dominated phase and the radiative cooling is irrelevant. On the other hand, FSRQs show a weak positive correlation between curvature and electron peak energy. The curvature of FSRQs evolves in a cooling dominated regime, where curvature correlates positive with peak energy. The strong cooling in FSRQs due to an additional EC component leads to higher curvature at the high energy tail of electron energy distribution. Thus, the true nature acceleration in FSRQs remains hidden.
Poster Title
The Evolution of Spectral Curvature of Fermi Bright Blazars
