Axion-like particle imprint in cosmological very-high-energy sources

TL;DR

This paper proposes that axion-like particles (ALPs) with ~1 neV mass can explain unexpected features in the spectra of distant VHE blazars, improving spectral fits over standard models.

Contribution

It demonstrates that including ALPs in models better explains VHE blazar spectra, providing evidence for ALPs affecting high-energy astrophysical observations.

Findings

Better spectral fits with ALPs than EBL-only models

Consistent critical energies for photon/ALP conversions across sources

Supports ALPs as a solution to VHE spectral anomalies

Abstract

Discoveries of very high energy (VHE) photons from distant blazars suggest that, after correction by extragalactic background light (EBL) absorption, there is a flatness or even a turn-up in their spectra at the highest energies that cannot be easily explained by the standard framework. Here, it is shown that a possible solution to this problem is achieved by assuming the existence of axion-like particles (ALPs) with masses ~1 neV. The ALP scenario is tested making use of observations of the highest redshift blazars known in the VHE energy regime, namely 3C 279, 3C 66A, PKS 1222+216 and PG 1553+113. In all cases, better fits to the observed spectra are found when including ALPs rather than considering EBL only. Interestingly, quite similar critical energies for photon/ALP conversions are also derived, independently of the source considered.