Modeling the Multiwavelength Spectral Energy Distributions of the Fermi-4LAC Bright Flat-spectrum Radio Quasars

Abstract

In this paper, we present a long-term multiwavelength investigation focusing on 12 distinct samples of Fermi-4LAC bright flat-spectrum radio quasars (FSRQs). Detailed variability and spectral analyses of γ-ray, X-ray, and ultraviolet/optical data obtained by the Fermi Large Area Telescope, the Swift X-ray Telescope, and the Swift Ultraviolet and Optical Telescope were performed over a period of about 14 yr, spanning from 2008 October to 2022 October. These analyses provide insights into characterizing the variations within different activity states. To efficiently reproduce the multiwavelength simultaneous/quasi-simultaneous spectral energy distributions (SEDs) of the samples, we propose a novel approach for constraining the model parameters. By analyzing the parameters of the energy spectral curvature (β), the peak frequency (ν pk), the peak luminosity (L pk), the Compton dominance parameter (A C), and the variability timescale (t var) in different activity states, we can estimate the values of the jet radiation region parameters for the samples. Subsequently, we utilize the synchrotron-self-Compton and external Compton processes, employing a logarithmic-parabolic spectral shape to approximate the observed spectra of the sample sources, while considering the induced regime for the physical parameters. The model results show that: (1) by effectively reproducing SEDs in various active states of bright FSRQs, the parameters within the emission region were reasonably constrained; (2) compared to other active states, the emission region of the jet exhibits a reduced radius during the high state, while the magnetic field strength increases during the low state; and (3) for bright FSRQs in a high-activity state, there is an enhancement of the Doppler factor, often exhibiting a tendency toward energy equipartition.

The Energy Budget in the Jet of High-frequency Peaked BL Lacertae Objects

“…Although the two subclasses exhibit numerous observational similarities, disparities in the characteristics of broad emission lines imply distinct physical mechanisms underlying the production of these lines. The multiwavelength spectral energy distributions (SEDs) of blazars show a typical double-hump structure (Inoue & Takahara 1996;Abdo et al 2010a;Ghisellini et al 2010;Kang et al 2014;Zheng et al 2019Zheng et al , 2020Xiong et al 2020;Zhou et al 2021Zhou et al , 2024Zhu et al 2021;Hu et al 2024). The lowenergy hump extends from the radio to the X-ray band, and its origin is effectively accounted for by synchrotron (Syn) mechanisms.…”