Constraints on the Optical-IR extragalactic background from gamma-ray absorption studies

TL;DR

This paper discusses how gamma-ray absorption studies can constrain the extragalactic background light independently of direct measurements, highlighting current limits and future prospects.

Contribution

It clarifies the relationship between gamma-ray spectra and background light constraints, and assesses the potential for future improvements in this method.

Findings

Gamma-ray absorption provides an independent constraint on diffuse background light.

Current limits depend on understanding gamma-ray source physics.

Future observations can improve these constraints.

Abstract

Very high energy (VHE) gamma-rays from extragalactic sources, interacting by gamma-gamma collisions with diffuse intergalactic radiation fields, provide an alternative way to constrain the diffuse background light, completely independent of direct measurements. The limits depend however on our knowledge of the physics of the gamma-ray sources. After clarifying the interplay between background light and VHE spectra, I summarize the extent and validity of the obtainable limits, and where future improvements can be expected.