The Gamma Ray Opacity of the Universe -- Indirect Measurements of the Extragalactic Background Light

TL;DR

This paper reviews recent indirect measurements of the Extragalactic Background Light (EBL) using gamma-ray absorption data, significantly reducing uncertainties in EBL intensity across 0.1 to 15 microns.

Contribution

It provides an overview of recent results that have narrowed down the uncertainties in EBL intensity measurements over a broad wavelength range.

Findings

Reduced uncertainties in EBL intensity from 0.1 to 15 microns.

Confirmation of gamma-ray absorption as an effective probe of EBL.

Improved constraints on the EBL spectrum.

Abstract

Indirect constraints on the intensity of the Extragalactic Background Light (EBL) were provided by recent studies of extragalactic sources emitting sub-TeV to multi-TeV photons. These constraints are provided thanks to the absorption of gamma rays by soft photons from the EBL (UV/optical/IR) via pair production by gamma - gamma interactions. This paper provides an overview of recent results that have led to substantially reduced uncertainties on the EBL intensity over a wide range of wavelengths from 0.1 to 15 micron.