Fermi Observations of Blazars: Implications for Gamma-ray Production
Abstract
The brightest blazars detected by the Fermi Gamma-ray Space Telescope Large Area Telescope (Fermi/LAT) show significant breaks in their spectra at a few GeV. The sharpness and the position of the breaks can be well reproduced by absorption of -rays via photon--photon pair production on He ii and H i Lyman recombination continua (LyC) produced in the broad-line region (BLR). Using 138 weeks of LAT observations of the brightest GeV blazar 3C 454.3 we find a power-law dependence of the peak energy on flux and discover anti-correlation between flux and the column density of the He ii LyC which is responsible for absorption of the >2.5 GeV photons in this object. The strength and the variability of the absorption implies the location of the gamma-ray emitting zone close to the boundary of the high-ionization part of the BLR and moving away from the black hole when the flux increases. A combination of the GeV breaks with the detection of a few powerful blazars in the TeV range puts strong constraints on the BLR size. Additional spectral breaks at ~100 and ~400 GeV due to absorption by the Balmer and Paschen lines could be detected by the Cherenkov Telescope Array.
Cite
@article{arxiv.1109.0946,
title = {Fermi Observations of Blazars: Implications for Gamma-ray Production},
author = {Juri Poutanen and Boris E. Stern},
journal= {arXiv preprint arXiv:1109.0946},
year = {2012}
}
Comments
10 pages, 5 figures, submitted to proceedings of AGN Physics in the CTA Era (AGN 2011), to be published in PoS