Multiwavelength Study of the Quiescent States of Six Brightest Flat Spectrum Radio Quasars detected by Fermi-LAT

TL;DR

This study analyzes the broadband spectral energy distributions of six bright flat-spectrum radio quasars during their quiescent states, revealing correlations between magnetic fields, emission region distances, and gamma-ray luminosity, and modeling their emission mechanisms.

Contribution

It provides the first detailed multi-wavelength SED modeling of these quasars in quiescent states, elucidating jet physics and disk-jet connections.

Findings

Magnetic field decreases with emission region distance and disk luminosity.

High-energy electron index correlates with gamma-ray luminosity.

Jets are radiatively inefficient during quiescent states.

Abstract

The regular monitoring of flat-spectrum radio quasars (FSRQs) in $\gamma$-rays by Fermi-LAT since past 12 years indicated six sources who exhibited extreme $\gamma$-ray outbursts crossing daily flux of $10^{-5}$ photons/cm$^{2}$/s. We obtained nearly-simultaneous multi-wavelength data of these sources in radio to $\gamma$-ray waveband from OVRO, Steward Observatory, SMARTS, Swift-UVOT, Swift-XRT, and Fermi-LAT. The time-averaged broadband Spectral Energy Distributions (SEDs) of these sources in quiescent states were studied to get an idea about the underlying baseline radiation processes. We modeled the SEDs using one-zone leptonic synchrotron and inverse-Compton emission scenario from broken power-law electron energy distribution inside a spherical plasma blob, relativistically moving down a conical jet. The model takes into account inverse-Compton scattering of externally and locally originated seed photons in the jet. The big blue bumps visible in quiescent state SEDs helped to estimate the accretion disk luminosities and central black hole masses. We found a correlation between the magnetic field inside the emission region and the ratio of emission region distance to disk luminosity, which implies that the magnetic field decreases with an increase in emission region distance and decrease in disk luminosity, suggesting a disk-jet connection. The high-energy index of the electron distribution was also found to be correlated with observed $\gamma$-ray luminosity as $\gamma$-rays are produced by high-energy particles. In most cases, kinetic power carried by electrons can account for jet radiation power as jets become radiatively inefficient during quiescent states.