Modeling the Multiwavelength Emission of 3C 279 during the 14 years of Fermi-LAT Era

TL;DR

This study analyzes 14 years of multiwavelength data from 3C 279, modeling its emission mechanisms and physical parameters to understand its variability and flaring behavior.

Contribution

It provides the first extensive broadband SED modeling of 3C 279 over 14 years, revealing the emission region's location and the role of Doppler beaming in flares.

Findings

Emission region is outside the BLR for most states.

Flares are caused by increased Doppler beaming and electron variation.

Emission region is near the outer boundary of the BLR during bright states.

Abstract

We report the results of our long-term multiwavelength spectral energy distribution (SED) study on the flat spectrum radio quasar 3C 279 during the $\sim14$ years (2008--2022) of {\sl Fermi}-LAT (Large Area Telescope) observing period. The {\sl Fermi}-LAT data were complemented with data in other wavebands obtained from {\sl Swift}-XRT/UVOT, Whole Earth Blazar Telescope (WEBT), along with other optical and radio data from several observatories. Different activity states were identified from the weekly binned $\gamma$-ray light curve, and it was possible to create 168 high-quality and quasi-simultaneous broadband SEDs. We modeled the SEDs using a one-zone leptonic scenario, including the emission region outside the broad-line region (BLR), involving synchrotron, synchrotron self-Compton, and external Compton mechanisms. Such extensive broadband modeling is essential for constraining the underlying multiwavelength radiative mechanisms in the 3C 279 jet and permits to estimate the physical parameters and explore their evolution in time. Our SED modeling study suggests that the increase in the Doppler beaming factor along with the variation of the emitting electrons is the cause for the flares in this source. The multiwavelength emission of 3C 279 was found to be well explained by the scenario in which the emission region is outside the BLR at a distance of $\sim6.42\times10^{3} R_S$. However, for two of the very bright $\gamma$-ray states, the emission region was found to be close to the outer boundary of the BLR at a distance of $\sim1.28\times10^{3} R_S$ from the central black hole.