Modeling the time variable spectral energy distribution of the blazar CTA 102 from 2008 to 2022

Abstract

We present long-term multiwavelength observations of blazar CTA 102 ($z=1.037$). Detailed temporal and spectral analyses of $\gamma$-ray, X-ray and UV/optical data observed by {\it Fermi}-LAT, Swift XRT, NuSTAR and Swift-UVOT over a period of 14 years, between August 2008 and March 2022, was performed. We found strong variability of source emission in all the considered bands, especially in the $\gamma$-ray band it exhibited extreme outbursts when the flux crossed the level of $10^{-5}\:{\rm photon\:cm^{-2}\:s^{-1}}$. Using the Bayesian Blocks algorithm, we split the adaptively binned $\gamma$-ray light curve into 347 intervals of quiescent and flaring episodes and for each period built corresponding multiwavelength spectral energy distributions (SEDs), using the available data. Among the considered SEDs, 117 high-quality (quasi) contemporaneous SEDs which have sufficient multiwavelength data, were modeled using JetSeT framework within a one-zone leptonic synchrotron and inverse Compton emission scenario assuming the emitting region is within the broad-line-region and considering internal and external seed photons for the inverse Compton up-scattering. As a result of modeling, the characteristics of the relativistic electron distribution in the jet as well as jet properties are retrieved and their variation in time is investigated. The applied model can adequately explain the assembled SEDs and the modelling shows that the data in the bright flaring periods can be reproduced for high Doppler boosting and magnetic field. The obtained results are discussed in the context of particle cooling in the emitting region.