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Title: The polarization dependence of γγ absorption—implications for γ-ray bursts and blazars

This paper presents an analysis of the dependence of the opacity for high-energy γ-rays to γγ absorption by low-energy photons on the polarization of the γ-ray and target photons. This process has so far only been considered using the polarization-averaged γγ absorption cross section. It is demonstrated that in the case of polarized γ-ray emission, subject to source-intrinsic γγ absorption by polarized target photons, this may lead to a slight overestimation of the γγ opacity by up to ∼10% in the case of a perfectly ordered magnetic field. Thus, for realistic astrophysical scenarios with partially ordered magnetic fields, the use of the polarization-averaged γγ cross section is justified for practical purposes, such as estimates of minimum Doppler factors inferred for γ-ray bursts and blazars, based on γγ transparency arguments; this paper quantifies the small error incurred by the unpolarized-radiation approximation. Furthermore, it is shown that polarization-dependent γγ absorption of initially polarized γ-rays can lead to a slight increase in the polarization beyond the spectral break caused by γγ absorption. This amount is distinctly different from the change in polarization expected if the same spectral break were produced by a break in the underlying electron distribution. This may serve as amore » diagnostic of whether γγ absorption is relevant in sources such as γ-ray bursts and blazars where the γ-ray emission may be intrinsically highly polarized.« less
Authors:
 [1]
  1. Centre for Space Research, North-West University, Potchefstroom 2520 (South Africa)
Publication Date:
OSTI Identifier:
22370344
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 795; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; APPROXIMATIONS; ASTROPHYSICS; COSMIC GAMMA BURSTS; CROSS SECTIONS; DISTRIBUTION; EMISSION; GALAXIES; GAMMA RADIATION; MAGNETIC FIELDS; OPACITY; PHOTONS; POLARIZATION; POLARIZED TARGETS; RELATIVISTIC RANGE; STARS