Absorption Features in Sub-TeV Gamma-Ray Spectra of BL Lac Objects

Abstract The production site of gamma rays in blazars is closely related to their interaction with the photon fields surrounding active galactic nucleus. In this paper, we discuss an indirect method that may help unveil presence ambient structures BL Lac objects through analysis gamma-ray spectrum. Gamma rays, passing at different distances from black hole, interact via γ pair corresponding and produce absorption features spectral energy distribution. An a putative broad-line region reduce flux only if its were very close central engine. However, jet photons bath optical-UV seed produced by narrow-line extended over parsec scale, consequent process cause detectable few hundreds GeV. detection such facilitated sources spectra reaching TeV energies, specifically HBLs EHBLs (extreme blazars) represent exceptional probes investigate topic. We recent observations extreme blazar named 2WHSP J073326.7+515354 (or PGC 2402248), which shows evidence feature spectrum narrow emission lines optical spectrum, suggesting regions large-scale environment. Finally, how sub-TeV affect broadband modeling eventually powerful diagnostic tool constrain