GeV-TeV $\gamma$-ray energy spectral break of BL Lac objects

TL;DR

This study analyzes the spectral breaks in BL Lac objects' gamma-ray emissions, finding evidence that both extragalactic background light attenuation and intrinsic curvature influence the observed spectral differences, with a focus on redshift evolution.

Contribution

It introduces a simple linear model linking spectral break to redshift, providing new insights into the roles of extragalactic background light and intrinsic curvature in gamma-ray spectra.

Findings

Spectral break correlates with redshift.

Both extragalactic background light and intrinsic curvature influence spectral breaks.

Redshift evolution is primarily due to extragalactic background light attenuation.

Abstract

In this paper, we compile the very-high-energy and high-energy spectral indices of 43 BL Lac objects from the literature. Based on a simple math model, $\Delta\Gamma_{obs}=\alpha {\rm{z}}+\beta $, we present evidence for the origin of an observed spectral break that is denoted by the difference between the observed very-high-energy and high-energy spectral indices, $\Delta\Gamma_{obs}$. We find by linear regression analysis that $\alpha\ne 0$ and $\beta\ne 0$. These results suggest that the extragalactic background light attenuation and the intrinsic curvature dominate on the GeV-TeV $\gamma$-ray energy spectral break of BL Lac objects. We argue that the extragalactic background light attenuation is an exclusive explanation for the redshift evolution of the observed spectral break.