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The EBL is strongly connected to gamma-ray astrophysics because high energy gamma-rays (E > 10 GeV) emitted by extragalactic sources are subject to absorption due to pair-production with EBL photons. One exciting consequence of this effect is that the magnitude of this absorption can then be used to measure (or at least constrain) the column density of background photons between the source and the observer [3]. This principle has been successfully applied by the H.E.S.S. collaboration [13] to constraint the EBL at Near-Infrared wavelengths, revealing at lower EBL flux than previously expected.
Due to the kinematics of pair-production, gamma-rays detected by ground-based telescopes (with energy E >~ 200 GeV) are subject to attenuation by the near- and mid-infrared part of the EBL. Gamma-ray absorption in this energy regime is quite strong, and therefore, probes of the EBL by ground-based instruments is limited to relatively low redshifts (z<~0.2). GLAST, on the other hand, is sensitive to the less drastic attenuation by the UV-optical part of the EBL, with no attenuation expected (at any redshift) for photons with energy below 10 GeV. Thus, EBL attenuation alone will not limit GLAST's ability to detect distant gamma-ray sources.
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[12] Komin, N., Piron, F., & Pelassa, V. 2007, in Proc. of the 1st GLAST Symposium
[13] Aharonian, F. et al., H.E.S.S. Collaboration, Nature, 440, 1018
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Figure 1. Schematic EBL spectrum as a function of wavelength. The EBL spectrum consists of two spectral humps: The blue hump at UV-Optical-NIR wavelengths is the radiated output from stars. The red hump at MIR (mid-infrared) and FIR (far-infrared) wavelengths results from the absorption and re-emission of starlight by the interstellar medium. The CMB spectrum (dashed black line) is presented here just for comparison purposes (since it is not considered part of the EBL). The location and size of the humps is just approximate, since the precise shape and intensity of the EBL is not completely constrained from observations.
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