# Measurement of the Extragalactic Background Light using MAGIC and Fermi-LAT gamma-ray observations of blazars up to z = 1

## TL;DR

This study measures the extragalactic background light (EBL) using gamma-ray observations of blazars up to redshift 1, confirming model predictions and hinting at a possible excess in certain wavelengths.

## Contribution

It provides the first joint likelihood analysis of 32 gamma-ray spectra from MAGIC and Fermi-LAT to estimate EBL density across a broad redshift range.

## Key findings

- EBL density estimates agree with current models.
- No evidence of universe transparency anomalies to gamma rays.
- Possible excess of EBL in 0.18-0.62 μm wavelength range.

## Abstract

We present a measurement of the extragalactic background light (EBL) based on a joint likelihood analysis of 32 gamma-ray spectra for 12 blazars in the redshift range z = 0.03 to 0.944, obtained by the MAGIC telescopes and Fermi-LAT. The EBL is the part of the diffuse extragalactic radiation spanning the ultraviolet, visible and infrared bands. Major contributors to the EBL are the light emitted by stars through the history of the universe, and the fraction of it which was absorbed by dust in galaxies and re-emitted at longer wavelengths. The EBL can be studied indirectly through its effect on very-high energy photons that are emitted by cosmic sources and absorbed via photon-photon interactions during their propagation across cosmological distances. We obtain estimates of the EBL density in good agreement with state-of-the-art models of the EBL production and evolution. The 1-sigma upper bounds, including systematic uncertainties, are between 13% and 23% above the nominal EBL density in the models. No anomaly in the expected transparency of the universe to gamma rays is observed in any range of optical depth.We also perform a wavelength-resolved EBL determination, which results in a hint of an excess of EBL in the 0.18 - 0.62 $\mu$m range relative to the studied models, yet compatible with them within systematics.