Indications for a pair-production anomaly from the propagation of VHE gamma-rays

By D. Horns, M. Meyer. 2012

157 citations recorded by the source corpus.

In the recent years, the number of detected very high energy (VHE: E > 100 GeV) gamma-ray sources has increased rapidly. The sources have been observed at redshifts up to z = 0.536 without strong indications for the presence of absorption features in the energy spectra. Absorption is however expected due to pair-production processes of the propagating photons with the photon bath in intergalactic space. Even though this photon density is not well known, lower limits can be firmly set by the resolved emission from galaxy counts. Using this guaranteed background light, we investigate the behaviour of the energy spectra in the transition region from the optically thin to the optically thick regime. Among the sample of 50 energy spectra, 7 spectra cover the the range from optical depth τ 2. For these sources, the transition to τ > 2 takes place at widely different energies ranging from 0.4 TeV to 21 TeV. Consistently, in all of these sources, an upturn of the absorption-corrected spectrum is visible at this transition with a combined significance of 4.2 standard deviations. Given the broad range of energies and redshifts covered by the sample, source-intrinsic features are unlikely to explain the observed effect. Systematic effects related to observations have been investigated and found to be not sufficient to account for the observed effect. The pair-production process seems to be suppressed in a similar way as expected in the extension of the standard model by a light ( < neV) pseudoscalar (axion-like) particle.

Subfields: Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/dfcb0c28968a4a66b53584414f867d7ca7a462aa

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Nuclear and High Energy Physics

Citations in the corpus

Any Light Particle Search II -- Technical Design Report (2013, background): “However, the observed energy spectra do not seem to match the absorption feature inferred from this argument [34].”
THE EXTRAGALACTIC BACKGROUND LIGHT, THE HUBBLE CONSTANT, AND ANOMALIES: CONCLUSIONS FROM 20 YEARS OF TeV GAMMA-RAY OBSERVATIONS (2015, methodology): “…of 1ES 1959+650 (Whipple, 2002), at 5.2,t = 3C 279 (MAGIC, 2006), at 4.2,t = and 1ES 0229 +200 (H.E.S.S., 2005–2006), at 6.7.t = They show flux enhancements of 13, 14, and even 23, respectively, but with uncertainties on the order of 100% that strongly bias the test devised by Horns & Meyer (2012).”
A hadronic origin for ultra-high-frequency-peaked BL Lac objects (2014, background): “There is already some evidence for a hardening of the TeV emission seen in the VHE spectra of BL Lac objects (Horns & Meyer 2012; Inoue et al. 2013).”
3FHL: The Third Catalog of Hard Fermi-LAT Sources (2017, background): “These photons permit testing EBL models and evaluating potential changes in the optical depth due to other more exotic scenarios (e.g., de Angelis et al. 2007; Sánchez-Conde et al. 2009; Essey & Kusenko 2010; Domínguez et al. 2011b; Horns & Meyer 2012).”
The extragalactic background light revisited and the cosmic photon–photon opacity (Corrigendum) (2017, methodology): “These analyses (see e.g., Horns & Meyer 2012; Costamante 2013) reported evidence for substantial upturns in the VHE spectra of Mkn 501 and Mkn 421, once corrected for pair-production absorption according to standard EBL models - like if such absorption corrections would be too large.”
The type IIB string axiverse and its low-energy phenomenology (2012, result): “For a recent compilation of the available data and comparison with the expectation, see [70].”
2FHL: THE SECOND CATALOG OF HARD FERMI-LAT SOURCES (2015, background): “These photons are especially interesting for testing alternative photon-propagation scenarios such as secondary cascades (Essey & Kusenko 2010) and axion-like particles (e.g.,de Angelis et al. 2007; SánchezConde et al. 2009; Domínguez et al. 2011a; Horns & Meyer 2012).”