Journal Article

Modification of the gamma-ray spectra by internal absorption in optically violently variable blazars: the example cases of 3C 273 and 3C 279

J. Sitarek and W. Bednarek

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 391, issue 2, pages 624-638
Published in print December 2008 | ISSN: 0035-8711
Published online November 2008 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.13771.x
Modification of the gamma-ray spectra by internal absorption in optically violently variable blazars: the example cases of 3C 273 and 3C 279

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Recent observations with the low-threshold Cherenkov telescopes proved that sub-TeV γ-rays are able to arrive from active galaxies at relatively large distances in spite of the expected severe absorption in the extragalactic background light (EBL). We calculate the γ-ray spectra at TeV energies from two example optically violently variable quasars, 3C 273 and 3C 279, assuming that γ-rays are injected in the inner parts of the jets launched by the accretion discs. It is assumed that γ-rays in the broad energy range (from MeV up to TeV) are produced in these blazars with a power-law spectrum with the spectral index as observed from these objects by the EGRET telescope at GeV energies. We take into account the internal absorption of these γ-rays by considering a number of models for the radiation field surrounding the jet. The classical picture of a relativistic blob in a jet for the injection of primary γ-rays is considered, with the injection rate of γ-rays as observed by the EGRET telescope in the GeV energy range. The results of calculations are compared with positive detection and the upper limits on the sub-TeV γ-ray fluxes from these two sources. It is concluded that, even with the Stecker EBL model, the level of γ-ray emission from 3C 279 is close to the recent measurements in the sub-TeV γ-ray energies, provided that the injected γ-ray spectrum extends from the GeV energies over the next two decades with this same spectral index. We also suggest that a flare with a time-scale of a few days from 3C 273 could be detected by the MAGIC II stereo telescopes.

Keywords: radiation mechanisms: non-thermal; galaxies: active; galaxies: individual: 3C 273; galaxies: individual: 3C 279; gamma-rays: theory

Journal Article.  10147 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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