Article

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

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

ABSTRACT

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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Available from: P. P. Temnikov, Oct 05, 2015
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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]. "
##### Article: The Quest for an Intermediate-Scale Accidental Axion and Further ALPs
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ABSTRACT: The recent detection of the cosmic microwave background polarimeter experiment BICEP2 of tensor fluctuations in the B-mode power spectrum basically excludes all plausible axion models where its decay constant is above $10^{13}$ GeV. Moreover, there are strong theoretical, astrophysical, and cosmological motivations for models involving, in addition to the axion, also axion-like particles (ALPs), with decay constants in the intermediate scale range, between $10^9$ GeV and $10^{13}$ GeV. Here, we present a general analysis of models with an axion and further ALPs and derive bounds on the relative size of the axion and ALP photon (and electron) coupling. We discuss what we can learn from measurements of the axion and ALP photon couplings about the fundamental parameters of the underlying ultraviolet completion of the theory. For the latter we consider extensions of the Standard Model in which the axion and the ALP(s) appear as pseudo Nambu-Goldstone bosons from the breaking of global chiral $U(1)$ (Peccei-Quinn (PQ)) symmetries, occuring accidentally as low energy remnants from exact discrete symmetries. In such models, the axion and the further ALP are protected from disastrous explicit symmetry breaking effects due to Planck-scale suppressed operators. The scenarios considered exploit heavy right handed neutrinos getting their mass via PQ symmetry breaking and thus explain the small mass of the active neutrinos via a seesaw relation between the electroweak and an intermediate PQ symmetry breaking scale. We show some models that can accommodate simultaneously an axion dark matter candidate, an ALP explaining the anomalous transparency of the universe for $\gamma$-rays, and an ALP explaining the recently reported 3.55 keV gamma line from galaxies and clusters of galaxies, if the respective decay constants are of intermediate scale.
Journal of High Energy Physics 03/2014; 2014(6). DOI:10.1007/JHEP06(2014)037 · 6.11 Impact Factor
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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]. "
##### Article: Anisotropy test of the axion-like particle Universe opacity effect: A case for the Cherenkov Telescope Array
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ABSTRACT: The Universe opacity to gamma rays is still an open question, in particular anomalies may have been observed. Assuming that such anomalies find their origin in conventional physics like intrinsic source spectra or the density of the extragalactic background light, they would be evenly distributed over the sky. If they exist, axion-like particles (ALPs) would have a potential effect on the opacity of the Universe to gamma rays, possibly related to the anomalies in the spectral indices of distant gamma-ray sources. In the scenario where ALPs from distant sources convert back to photons in the Galactic magnetic field, their effect on the opacity is expected to depend on the position of the sources. In that case the anomaly is expected to exhibit peculiar correlations on the sky. We propose a method to test the origin of the opacity anomaly, based on angular correlations of spectral softening anomalies. Such a diagnosis requires a wide-field survey of high-energy gamma-ray sources over a broad range of energy. The future Cherenkov Telescope Array (CTA) is perfectly suited to perform such a study. It is shown that while the current sample of sources is not large enough to base conclusions on, with this method CTA will be sensitive to ALP couplings to gamma rays of the order of 3e-11 GeV^-1 for ALP masses below 1e-8 eV.
Journal of Cosmology and Astroparticle Physics 09/2013; 2014(01). DOI:10.1088/1475-7516/2014/01/016 · 5.81 Impact Factor
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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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