Measurement of the expansion rate of the Universe from \gamma-ray attenuation

TL;DR

This paper measures the Universe's expansion rate using gamma-ray attenuation data, providing a novel method that aligns with existing measurements and demonstrates gamma-ray astronomy's potential for cosmology.

Contribution

It introduces a new technique to determine the Hubble constant from gamma-ray observations, expanding the tools available for cosmological measurements.

Findings

Hubble constant estimated at 71.8 km/s/Mpc with uncertainties.

Gamma-ray attenuation measurements are compatible with traditional methods.

The approach shows promise for future cosmological studies with advanced telescopes.

Abstract

A measurement of the expansion rate of the Universe (that is the Hubble constant, H0) is derived here using the gamma-ray attenuation observed in the spectra of gamma-ray sources produced by the interaction of extragalactic gamma-ray photons with the photons of the extragalactic background light (EBL). The Hubble constant that is determined with our technique, for a Lambda CDM cosmology, is H0=71.8_{-5.6}^{+4.6}(stat)_{-13.8}^{+7.2}(syst) km s^{-1} Mpc^{-1}. This value is compatible with present-day measurements using well established methods such as local distance ladders and cosmological probes. The recent detection of the cosmic gamma-ray horizon (CGRH) from multiwavelength observation of blazars, together with the advances in the knowledge of the EBL, allow us to measure the expansion rate of the Universe. This estimate of the Hubble constant shows that gamma-ray astronomy has reached a mature enough state to provide cosmological measurements, which may become more competitive in the future with the construction of the Cherenkov Telescope Array. We find that the maximum dependence of the CGRH on the Hubble constant is approximately between redshifts 0.04 and 0.1, thus this is a smoking gun for planning future observational efforts. Other cosmological parameters, such as the total dark matter density Omega_m and the dark energy equation of state w, are explored as well.