Measurement of the extragalactic background light imprint on the spectra of the brightest blazars observed with H.E.S.S

TL;DR

This study measures the imprint of the extragalactic background light on gamma-ray spectra of bright blazars using H.E.S.S., achieving the first high-confidence detection of EBL effects at very-high energies.

Contribution

It introduces a novel joint fitting method to measure EBL optical depth and intrinsic source spectra, providing the first high-confidence EBL measurement at energies above 100 GeV.

Findings

Detected EBL signature at 8.8 sigma significance

Constrained EBL flux density over 0.30-17 microns

Derived peak EBL flux at 1.4 microns as 15 +/- 2 (stat) +/- 3 (sys) nW/m^2/sr

Abstract

The extragalactic background light (EBL) is the diffuse radiation with the second highest energy density in the Universe after the cosmic microwave background. The aim of this study is the measurement of the imprint of the EBL opacity to gamma-rays on the spectra of the brightest extragalactic sources detected with the High Energy Stereoscopic System (H.E.S.S.). The originality of the method lies in the joint fit of the EBL optical depth and of the intrinsic spectra of the sources, assuming intrinsic smoothness. Analysis of a total of ~10^5 gamma-ray events enables the detection of an EBL signature at the 8.8 std dev level and constitutes the first measurement of the EBL optical depth using very-high energy (E>100 GeV) gamma-rays. The EBL flux density is constrained over almost two decades of wavelengths (0.30-17 microns) and the peak value at 1.4 micron is derived as 15 +/- 2 (stat) +/- 3 (sys) nW / m^2 sr.