Temporal and Spectral Variabilities of High‐Energy Emission from Blazars Using Synchrotron Self‐Compton Models

Abstract

Multiwavelength observations of blazars such as Mrk 421 and Mrk 501 show that they exhibit strong short time variabilities in flare-like phenomena. Based on the homogeneous synchrotron self-Compton (SSC) model and assuming that time variability of the emission is initiated by changes in the injection of nonthermal electrons, we perform detailed temporal and spectral studies of a purely cooling plasma system, using parameters appropriate to blazars. One important parameter is the total injected energy E and we show how the synchrotron and Compton components respond as E varies. When the synchrotron and SSC components have comparable peak fluxes, we find that the SSC process contributes strongly to the electron cooling and the whole system is nonlinear, thus simultaneously solving electron and photon kinetic equations is necessary. In the limit of the injection-dominated situation when the cooling timescale is long, we find a unique set of model parameters that are fully constrained by observable quantities. In the limit of cooling-dominated situation, TeV emissions arise mostly from a cooled electron distribution and Compton scattering process is always in the Klein-Nishina regime, which makes the TeV spectrum having a large curvature. Furthermore, even in a single injection event, the multiwavelength light-curves do not necessarily track each other because the electrons that are responsible for those emissions might have quite different lifetimes. We discuss in detail how one could infer important physical parameters using the observed spectra. In particular, we could infer the size of the emission region by looking for exponential decay in the light curves. We could also test the basic assumption of SSC by measuring the difference in the rate of peak energy changes of synchrotron and SSC peaks. We also show that the trajectory in the photon-index-flux plane evolves clockwise or counter-clockwise depending on the value of E and observed energy bands.

Variability Timescales of TeV Blazars Observed in theASCAContinuous Long‐Look X‐Ray Monitoring

“…The time series we are comparing here are certainly due to the same electron population cooling via a common radiation process ; in our case, this is primarily synchrotron emission, where the rate of electron energy loss is dependent on that energy. (Compton cooling for this energy range of electron is strongly suppressed by the Klein-Nishina cuto † ; e.g., Kataoka 2000 ;Li & Kusunose 2000. ) If cooling or acceleration is the cause of lags, as it is often interpreted, the di †erence is likely to arise in the decay or rise timescales of the Ñares, and what we want to verify and quantify is the energy dependence.…”

Modeling the emission processes in blazars

“…BL Lac objects occasionally exhibit X-ray variability patterns which can be characterized as spectral hysteresis in hardness-intensity diagrams (e.g., [85,36,25,91]). This has been interpreted as the synchrotron signature of gradual injection and/or acceleration of ultrarelativistic electrons in the emitting region, and subsequent radiative cooling (e.g., [39,27,36,43,45,9]). While spectral hysteresis has so far only been clearly identified in HBLs, it should also occur in the soft X-ray emission of LBLs if their synchrotron component extends into the soft Xray regime.…”

Modelling blazar flaring using a time-dependent fluid jet emission model – an explanation for orphan flares and radio lags

“…Previous work modelling flaring behaviour has focused on using one or two physically disconnected spherical emission regions to model flares, with varying success depending on the properties of the flare (e.g. Kirk et al 1998Li & Kusunose 2000Böttcher & Chiang 2002, Błażejowski et al 2005, Finke et al 2008Nalewajko et al 2012and Petropoulou 2014. More recently, multizone models have been developed to try to understand the stochastic nature of the variability and polarisation (e.g.…”