<> "The repository administrator has not yet configured an RDF license."^^ . <> . . "Effects of EBL extinction on the VHE spectra of blazars"^^ . "Active 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 which generates this tremendous luminosity. The Very High Energy (VHE; E>100 GeV) photons from blazars while travelling through the intergalactic medium, interact with the low energy photons (in the UV-IR range) constituting the Extragalactic Background Light (EBL), by producing e-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 difficult to detect distant sources. This phenomena gives us the means to measure the EBL level which cannot be directly measured. In this thesis the effects of EBL absorption on the spectra of blazars is studied. Two methods to discover distant VHE blazars were explored. The observations with HESS led to the detection of the blazar PKS 1510-089 at z=0.36, at a 4.8 sigma level. A cross check analysis with a more advanced analysis tool confirmed this detection at a 8.5 sigma level. The GeV spectrum obtained by analyzing Fermi GST data, was adopted as the intrinsic source spectrum. Models for the gamma-ray spectrum including the EBL absorption was fitted to the gamma-ray data and it was shown that all the 4 current EBL models considered here, fit the data well. It is concluded that this is due to the sensitivity limits of the current VHE instruments. Stronger constraints on the EBL would only be possible for sources with much harder spectrum. The outlook for future experiments is discussed. EBL extinction causes bias in the sample of detected blazars. MonteCarlo simulations were used to generate parent samples for the VHE blazars. These were compared to the true VHE blazar sample and constraints on the parent sample properties were drawn. The lack of a spectral softening with z in the true VHE sample, is found consistent with a parent sample that clearly shows this softening, making it unnecessary to assume any special dependence of the intrinsic spectral index on z. The dependence of the evolution of the EBL on the cosmological model considered, was explored. The uncertainty in cosmology was found to be negligible compared to the uncertainty on the EBL. The dependence of the extinction on the error in the EBL models as well as the effect of neglecting the EBL evolution with z was illustrated."^^ . "2010" . . . . . . . . "Bagmeet"^^ . "Behera"^^ . "Bagmeet Behera"^^ . . . . . . "Effects of EBL extinction on the VHE spectra of blazars (PDF)"^^ . . . "Bagmeet_thesis.pdf"^^ . . . "Effects of EBL extinction on the VHE spectra of blazars (Other)"^^ . . . . . . "indexcodes.txt"^^ . . . "Effects of EBL extinction on the VHE spectra of blazars (Other)"^^ . . . . . . "lightbox.jpg"^^ . . . "Effects of EBL extinction on the VHE spectra of blazars (Other)"^^ . . . . . . "preview.jpg"^^ . . . "Effects of EBL extinction on the VHE spectra of blazars (Other)"^^ . . . . . . "medium.jpg"^^ . . . "Effects of EBL extinction on the VHE spectra of blazars (Other)"^^ . . . . . . "small.jpg"^^ . . "HTML Summary of #10454 \n\nEffects of EBL extinction on the VHE spectra of blazars\n\n" . "text/html" . . . "520 Astronomie"@de . "520 Astronomy and allied sciences"@en . .