Constraining blazars distances with combined GeV and TeV data

TL;DR

This paper presents a method to estimate blazar distances by combining GeV and TeV gamma-ray data, utilizing spectral absorption features to infer redshifts for sources with unknown distances.

Contribution

The paper refines a novel approach that constrains blazar redshifts by analyzing combined GeV and TeV spectra, applying it to new data and an unknown-distance blazar.

Findings

Revised the sample with updated spectra in GeV and TeV bands.

Applied the method to PKS 1424+240, estimating its redshift.

Confirmed the linear relation between spectral constraints and redshift.

Abstract

Recently, a new method to constrain the distances of blazars with unknown redshift using combined observations in the GeV and TeV regimes has been developed. The underlying assumption is that the Very High Energy (VHE, E > 100 GeV) spectrum corrected for the absorption of TeV photons by the Extragalactic Background Light (EBL) via photon-photon interaction should still be softer than the gamma-ray spectrum observed by Fermi/LAT. The constraints found are related to the real redshifts by a simple linear relation, that has been used to infer the unknown or uncertain distance of blazars. The sample is revised with the up-to-date spectra in both TeV and GeV bands and the method applied to the unknown distance blazar PKS 1424+240 detected at VHE.