Cosmology from very high energy $\gamma$-rays

TL;DR

This paper explores how very high energy gamma-ray observations of blazars can be used as an independent method to constrain the Hubble constant, providing results consistent with existing measurements.

Contribution

It introduces a novel approach using gamma-ray attenuation to estimate the Hubble constant, differing from traditional methods like supernovae and CMB observations.

Findings

Hubble constant constrained to be consistent with other methods at 2σ level.

VHE gamma-ray attenuation can serve as a cosmological distance indicator.

Study of two blazars supports the viability of this method.

Abstract

In this work we study how the cosmological parameter, the Hubble constant $H_0$, can be constrained by observation of very high energy (VHE) $\gamma$-rays at the TeV scale. The VHE $\gamma$-rays experience attenuation by background radiation field through $e^+e^-$ pair production during the propagation in the intergalactic space. This effect is proportional to the distance that the VHE $\gamma$-rays go through. Therefore the absorption of TeV $\gamma$-rays can be taken as cosmological distance indicator to constrain the cosmological parameters. Two blazars Mrk 501 and 1ES 1101-232, which have relatively good spectra measurements by the atmospheric Cerenkov telescope, are studied to constrain $H_0$. The mechanism constraining the Hubble constant adopted here is very different from the previous methods such as the observations of type Ia supernovae and the cosmic microwave background. However, at $2\sigma$ level, our result is consistent with other methods.