Abdo 2010 用LAT的GeV光子观测限制河外背景光子

主要内容:

高能光子会和河外背景光子湮灭产生正负电子对。如果背景光子足够多，就看不到来自于很远的高能光子了。由于看到了一些高能光子，限制了一些说会有很多背景光子的模型。

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Title:		Fermi-LAT Constraints on the Gamma-ray Opacity of the Universe
Authors:		Fermi LAT, The; the GBM Collaboration: A. A. Abdo
Publication:		eprint arXiv:1005.0996
Publication Date:		05/2010
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		39 pages, 11 figures, submitted to ApJ; Corresponding authors: A. Bouvier, A. Chen, S. Raino, S. Razzaque, A. Reimer, L. C. Reyes
Bibliographic Code:		2010arXiv1005.0996F

Abstract

The Extragalactic Background Light (EBL) includes photons with wavelengths from ultraviolet to infrared, which are effective at attenuating gamma rays with energy above ~10 GeV during propagation from sources at cosmological distances. This results in a redshift- and energy-dependent attenuation of the gamma-ray flux of extragalactic sources such as blazars and Gamma-Ray Bursts (GRBs). The Large Area Telescope onboard Fermi detects a sample of gamma-ray blazars with redshift up to z~3, and GRBs with redshift up to z~4.3. Using photons above 10 GeV collected by Fermi over more than one year of observations for these sources, we investigate the effects of the EBL on the gamma-ray flux. We constrain the gamma-ray opacity of the Universe at various energies and redshifts, and compare this with predictions from well-known EBL models. We find that an EBL intensity in the optical-ultraviolet wavelengths as great as predicted by the "fast-evolution" and "baseline" models of Stecker et al (2006) can be ruled out with high confidence.

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