Study On The Gev-TeV Spectral Formation Mechanism Of BL Lacs

The TeV gamma photons from BL Lacs may interact with interstellar infrared-ultraviolet photons to generate electron-positron pair(γ+ γ→e+ + e-)when propagate to the observer,resulting in observed spectrum becomes soft.In the lower energy-GeV gamma-ray energy,the photon energy is low and cannot be absorbed by the extragalactic galaxy background light.The GeV gamma ray spectral curvature is different from the TeV gamma ray spectral curvature(the spectral index is different).However,in addition to the inverse Compton scattering in the jet radiation,the GeV-TeV gamma ray spectrum of BL Lac objects may also be generated in various electromagnetic cascade processes,which make the GeV-TeV gamma ray spectral"break" causes many uncertainties.In order to determine whether the extragalactic galaxy background light absorption is an origin of GeV-TeV gamma-ray energy spectral "break" in the high redshift,we performed the following work:(1)Establish a simple mathematical model,△Γobs=αz+β.This model divides the difference between the TeV gamma-ray and the GeV gamma-ray energy spectral index into two parts:az relates to the redshift and β has nothing to do with the redshift.This model shows that:if α≠0,β=0,we study the relationship between the extragalactic background light attenuation with redshift;if α ≠ 0,β≠0,we study the origin of the observed spectral break.Both the extragalactic background light attenuation and some physical processes(intrinsic spectral curvature)contribute to the observed spectral break;if α ≠ 0,β≠0,we study the origin of the intrinsic spectral break which only effect by some physical processes(intrinsic spectral curvature).(2)We compile the observed spectral indices of 126 BL Lac objects in the high energy and very high energy,and analyze the relationship between △Γobs and the redshift z.The statistical analysis results showed that:α ≠ 0,β≠0.(3)Removed the source of TeV gamma ray radiation was not observed in the sample,and analyzed the relationship between △Γobs and the redshift z.Statistical analysis results show:α ≠ 0,β≠0.Our statistical results show that both the the extragalactic background attenuation and some physical processes contribute to the GeV-TeV gamma ray spectral break of BL Lac objects.