# Measurement of the Extragalactic Background Light with VERITAS

## TL;DR

This paper reports on measuring the extragalactic background light (EBL) using 10 years of VERITAS gamma-ray observations of blazars, providing new constraints on the cosmic infrared background.

## Contribution

It introduces a method to measure the EBL spectrum independently of its assumed shape, utilizing gamma-ray spectra from blazars and accounting for uncertainties.

## Key findings

- Measured EBL spectrum consistent with galaxy count lower limits
- Constrained the cosmic infrared background in the 0.56-56 μm range
- Limited the contribution from diffuse components to the EBL

## Abstract

The extragalactic background light records the history of infrared, optical and ultraviolet light radiation including re-radiation since the epoch of reionization. While challenging to measure directly, it can be measured indirectly via its impact on observed spectra of extragalactic gamma-ray emitters. VERITAS, a ground-based imaging atmospheric-Cherenkov telescope array sensitive to gamma rays above 100 GeV, has accrued 10 years of observations of hard-spectrum blazars. The energy and redshift range covered enables the measurement of the EBL in the range 0.56-56~$\mu$m, accessing the poorly constrained cosmic infrared background region. New constraints on the EBL resulting from the joint analysis using 16 spectra from 14 VERITAS-observed blazars will be presented. The method is independent of assumptions about the shape of the EBL spectrum, and includes a full treatment of systematic and statistical uncertainties. The measured spectrum is in good agreement with lower limits from galaxy counts, limiting the potential contribution from a diffuse component.