Very-high-energy gamma-ray emission from high-redshift blazars

TL;DR

This study investigates the detection prospects of very high-energy gamma-ray emission from high-redshift blazars using Fermi data, identifying several potential sources for ground-based telescopes and discussing observational challenges.

Contribution

It reports the detection of VHE gamma-ray flux from thirteen high-redshift blazars and assesses their detectability with current and future ground-based gamma-ray telescopes.

Findings

Thirteen high-redshift sources detected in VHE gamma rays by Fermi.

Detection with ground-based telescopes is challenging but feasible for certain sources.

Future high-altitude Cherenkov telescopes could enable high-statistics studies of distant VHE sources.

Abstract

We study the possible detection of and properties of very high-energy (VHE) gamma-ray emission (in the energy band above 100 GeV) from high redshift sources. We report on the detection of VHE gamma-ray flux from blazars with redshifts z>0.5. We use the data of Fermi telescope in the energy band above 100 GeV and identify significant sources via cross-correlation of arrival directions of individual VHE gamma-rays with the positions of known Fermi sources. There are thirteen high-redshift sources detected in the VHE band by Fermi/LAT telescope. The present statistics of the Fermi signal from these sources is too low for a sensible study of the effects of suppression of the VHE flux by pair production through interactions with Extragalactic Background Light photons. We find that the detection of these sources with ground-based gamma-ray telescopes would be challenging. However, several sources including BL Lacs PKS 0426-380 at z=1.11, KUV 00311-1938 at z=0.61, B3 1307+433 at z=0.69, PG 1246+586 at z=0.84, Ton 116 at z=1.065 as well as a flat-spectrum radio quasar 4C +55.17 at z=0.89 should be detectable by HESS-II, MAGIC-II and CTA. A high-statistics study of a much larger number of VHE gamma-ray sources at cosmological distances would be possible with the proposed high-altitude Cherenkov telescope 5@5.