Transparency of the Universe to gamma-rays

Abstract

Using the most recent observational data concerning the Extragalactic Background Light and the Radio Background, for a source at a redshift z s ≤ 3 we compute the energy E 0 of an observed γ-ray photon in the range 10 GeV ≤ E 0 ≤ 10 13 GeV such that the resulting optical depth τ γ (E 0 , z s ) takes the values 1, 2, 3 and 4.6, corresponding to an observed flux dimming of e −1 0.37, e −2 0.14, e −3 0.05 and e −4.6 0.01, respectively. Below a source distance D 8 kpc we find that τ γ (E 0 , DH 0 /c) < 1 for any value of E 0 . In the limiting case of a local Universe (z s 0) we compare our result with the one derived in 1997 by Coppi and Aharonian. The present achievement is of paramount relevance for the planned ground-based detectors like CTA, HAWC and HiSCORE.

Restrictions from Lorentz invariance violation on cosmic ray propagation

“…(2). To be specific, we have chosen two representative and relevant processes for cosmic ray physics: pair photo production and pion photo production [44][45][46][47],…”

Limits on the Lorentz Invariance Violation from UHECR Astrophysics

“…For the RB, the data from Gervasi et al (2008) with a cutoff at 1 MHz were used. Different cutoffs in the RB data lead to different photon horizons as shown in reference De Angelis et al (2013). Since no new effect shows up in the LIV calculation due to the RB cutoff, only the 1 MHz cutoff will be presented.…”

“…In this section, the photon horizon is calculated including LIV effects. The argument presented in reference De Angelis et al (2013) is followed here.…”

“…Lorentz invariant gamma-ray propagation in the intergalactic photon background was studied previously in detail by De Angelis et al (2013), a similar approach is followed in section 2, but LIV is allowed in the interaction of high energy photons with the background light and their consequences are studied. The process γγ → e + e − is the only one considered to violate Lorentz invariance, and as a similar approach used in Galaverni & Sigl (2008a), such LIV correction can lead to a correction of the LI energy threshold of the production process.…”

Report from the Multi-Messenger Working Group at UHECR-2014 Conference

“…Since photon induced air-showers exhibit specific characteristics, the sensitivity for detection can additionally be improved by selecting only "photon-like" events. Compared to EeV neutrons, the detectable volume is large enough to encompass in addition to the Milky Way, the Local Group of galaxies, and possibly Centaurus A, given an attenuation length of about 4.5 Mpc at EeV energies [73][74][75].…”