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

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.