Constraining the location of rapid gamma-ray flares in the FSRQ 3C 273

TL;DR

This study analyzes rapid gamma-ray flares in quasar 3C 273, constraining the emission region’s location and size, and revealing spectral breaks and multiple shock scenarios within the jet.

Contribution

It provides new constraints on the gamma-ray emission region’s size and location in 3C 273 using rapid flare variability and spectral analysis.

Findings

Gamma-ray emission region is within 1.6 pc of the central source.

Rapid flare with a flux doubling time of 1.1 hours observed.

Spectral breaks in the 1-2 GeV range linked to emission processes.

Abstract

We present a \gamma-ray photon flux and spectral variability study of the flat-spectrum radio quasar 3C 273 over a rapid flaring activity period between September 2009 to April 2010. Five major flares are observed in the source during this period. The most rapid flare observed in the source has a flux doubling time of 1.1 hr. The rapid \gamma-ray flares allow us to constrain the location and size of the \gamma-ray emission region in the source. The \gamma \gamma-opacity constrains the Doppler factor, $\delta_{\gamma} \geq$ 10 for the highest energy (15 GeV) photon observed by the {\it Fermi}-Large Area Telescope (LAT). Causality arguments constrain the size of the emission region to 1.6$\times 10^{15}$ cm. The \gamma-ray spectra measured over this period show clear deviations from a simple power law with a break in 1-2 GeV energy range. We discuss possible explanations for the origin of the \gamma-ray spectral breaks. Our study suggests that the \gamma-ray emission region in 3C 273 is located within the broad line region ($<$1.6 pc). The spectral behavior and temporal characteristics of the individual flares indicate the presence of multiple shock scenarios at the base of the jet.