Redshift of the Blazar KUV 00311-1938: Modeling the EBL Absorption

Abstract

AGNs are believed to be the source of very energetic cosmic rays which, in turn, produce gamma rays throughout the interactions with matter. Therefore, the study of their very-high-energy (VHE) gamma-ray spectra is fundamental to understand the cosmic-ray acceleration mechanisms in these objects. Blazars are the most common type of AGNs populating gamma-ray catalogs, among these sources BL-Lacs present featureless or very weak emission/absorption lines spectra. Given that the extragalactic VHE gamma-ray catalog is poorly populated (about 70 blazars), having a redshift estimation of every single source is important for the study of cosmic rays origin. In this work we use EBL absorption as a tool to estimate KUV 00311-1938 redshift by comparing HE gamma-ray observations with modeled EBL absorbed flux points. KUV 00311-1938 is a very interesting BL-Lac; a priori it can be one of the most distant blazars since it has an estimated redshift in the range 0.5 to 1.54. Assuming that there is no spectral cutoff, we consider the intrinsic VHE spectrum to be the extrapolation of the Fermi-LAT spectrum and model the intergalactic absorption by using the main current EBL models. Comparing these results with the VHE measured point by H.E.S.S., we give an estimate for the redshift of the blazar within observation errors.