Intrinsic absorption in 3C 279 at GeV-TeV energies and consequences for estimates of the EBL

TL;DR

This paper investigates gamma-ray absorption in quasar 3C 279's broad line region to refine estimates of the extragalactic background light, confirming the robustness of current EBL upper limit methods.

Contribution

It introduces detailed modeling of gamma-ray absorption within the quasar's broad line region using CLOUDY, assessing its impact on EBL measurements.

Findings

Absorption inside the BLR does not significantly harden the gamma-ray spectrum.

The method for deriving EBL upper limits remains valid despite internal absorption.

Gamma-ray photons are less affected by BLR absorption than previously thought.

Abstract

We revisit the limits of the level of the extragalactic background light (EBL) recently reported by the MAGIC collaboration based on the observed gamma-ray spectrum of the quasar 3C279, considering the impact of absorption of high-energy gamma-ray photons inside the broad line region (BLR) of the quasar. We use the photoionization code CLOUDY to calculate the expected optical-UV radiation field inside the BLR and the optical depth to gamma-rays for a relatively extended set of the parameters. We found that the absorption of gamma-ray photons, though important for the estimate of the true radiative output of the source, does not produce an important hardening of the spectrum of 3C279 in the energy band accessible by MAGIC, supporting the method used to infer the upper limits to the level of the EBL.