Absorption of 10 Gev--1 Tev Gamma Rays from 3C 279

TL;DR

This study analyzes gamma-ray absorption in 3C 279 to determine the emission region, suggesting it is likely within the BLR shell, which impacts understanding of gamma-ray production mechanisms.

Contribution

It provides new constraints on the gamma-ray emitting region in 3C 279 by analyzing photon-photon absorption, challenging previous models of emission location.

Findings

Gamma-ray emission region likely within the BLR shell.

Absorption analysis constrains the emission site closer to the inner BLR radius.

Results are consistent with previous findings and challenge some existing models.

Abstract

In this paper, we revisit gamma-ray--emitting region for 10 GeV--1 TeV gamma rays from 3C 279 through studying the photon-photon absorption optical depth due to the diffuse radiation of the broad-line region (BLR) and the extragalactic background light (EBL). Based on the power-law spectrum detected by MAGIC, the preabsorbed spectra are inferred by correcting the photon-photon absorption on the diffuse photons of the BLR (internal absorption) and the EBL (external absorption). Position of gamma-ray emitting region $R_{\rm{\gamma}}$ determines the relative contributions of this two diffuse radiation to the total absorption. Our results indicate that $R_{\rm{\gamma}}$ may be within the BLR shell for 3C 279, likely closer to the inner radius, which is consistent with our previous results. This is neither consistent with the suggestions of B\"ottcher et al. (2008b), that VHE gamma-ray emission is produced far outside the BLR, nor with the assumptions of Tavecchio & Mazin (2008), that VHE gamma-ray--emitting region is inside the BLR cavity. $R_{\rm{\gamma}}$ is a key physical quantity that could set some constraints on emission mechanisms that produce the VHE gamma rays from 3C 279. Observations of $\it Fermi$-LAT, MAGIC, HESS, and VERITAS in the near future could give more constraints on the position of gamma-ray emitting region relative to the BLR.