Very-High-Energy Gamma Rays from a Distant Quasar: How Transparent Is the Universe?

Universität Würzburg, D-97074 Würzburg, Germany.
Science (Impact Factor: 33.61). 07/2008; 320(5884):1752-4. DOI: 10.1126/science.1157087
Source: PubMed


The atmospheric Cherenkov gamma-ray telescope MAGIC, designed for a low-energy threshold, has detected very-high-energy gamma
rays from a giant flare of the distant Quasi-Stellar Radio Source (in short: radio quasar) 3C 279, at a distance of more than
5 billion light-years (a redshift of 0.536). No quasar has been observed previously in very-high-energy gamma radiation, and
this is also the most distant object detected emitting gamma rays above 50 gigaelectron volts. Because high-energy gamma rays
may be stopped by interacting with the diffuse background light in the universe, the observations by MAGIC imply a low amount
for such light, consistent with that known from galaxy counts.

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    • "The recent detection of this effect by Fermi [70] and H.E.S.S. [71] has allowed to constrain the EBL density. At large optical depth, τ 2, however, there are hints that the Universe is anomalously transparent to gamma-rays [72] [73] [74] [75] [76]. This may be explained by photon ↔ ALP oscillations: the conversion of gamma rays into ALPs in the magnetic fields around AGNs or in the intergalactic medium, followed by their unimpeded travel towards our galaxy and the consequent reconversion into photons in the galactic/intergalactic magnetic fields [77] [78] [79] [80] [81]. "
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    • "Without these measurements, or if one wishes to infer more precise effects, it is necessary to rely on models for the evolution of the EBL density with redshift (for a review, see [18]). As previously mentioned, the observation of sources at redshifts up to ∼0.5 with IACTs challenged this interpretation of the extragalactic absorption [15] [16] [39]. Although the recent measurements by H.E.S.S. (see also [40]) seem not in conflict with the most recent EBL models, some studies still show evidence for a pair-production anomaly [14] [26]. "
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    • "Consequently, the spectral energy cutoff can be a probe for the EBL density. Measurements deliver a relatively high cutoff energy compared to current EBL model predictions [30]. This can be an indicator for physics beyond the standard model [31]. "

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