Effects of EBL extinction on the VHE spectra of blazars [Elektronische Ressource] / put forward by Bagmeet Behera

Dissertationsubmitted to theCombined Faculties for the Natural Sciences and for Mathematicsof the Ruperto-Carola University of Heidelberg, Germanyfor the degree ofDoctor of Natural SciencesPut forward byMaster of Science: Bagmeet Beheraborn in: Rourkela, IndiathOral examination: 9 February, 2010E ects of EBL extinctionon the VHE spectra of blazarsReferees: Prof. Dr. Stefan J. WagnerProf. Dr. Werner HofmannAbstractActive Galactic Nuclei (AGN) are the most powerful steady sources of electromagnetic radiation in the cosmos.Blazars are AGN with their jets pointing straight at us, giving us the opportunity to probe deep into the core whichgenerates this tremendous luminosity. The Very High Energy (VHE; E > 100GeV ) photons from blazars whiletravelling through the intergalactic medium, interact with the low energy photons (in the UV-IR range) constituting+the Extragalactic Background Light (EBL), by producinge e pairs, and get absorbed. More than 25 nearby blazars(z < 0:3) have been detected in VHE, but due to EBL extinction it is extremely di cult to detect distant sources.This phenomena gives us the means to measure the EBL level which cannot be directly measured. In this thesisthe e ects of EBL absorption on the spectra of blazars is studied. Two methods to discover distant VHE blazarswere explored. The observations with HESS led to the detection of the blazar PKS 1510-089 at z = 0:36, at a 4.8level.