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Development of New Composite Mirrors for Imaging Cherenkov Telescopes and Observations of the Two Blazar Objects 1ES 0806+524 and 1ES 1011+496 with MAGIC

This PhD thesis is addressed to the technical and scientific studies carried out in the research field of very high energy (VHE, E > 100GeV) gamma-ray astronomy, a promising discipline which is extending the frontier of our knowledge of the emission by extraterrestrial sources to the highest observable energies of the electromagnetic spectrum. 
 
Radio--loud active galactic nuclei (AGNs) are astronomical objects whose emission along relativistic jets is powered by the accretion of matter onto the disk of a supermassive black hole. Depending on the orientation of their relativistic jets, radio--loud AGNs are divided into two categories, among them the so--called blazars. Such objects present one jet oriented at small angles with respect to the line of sight of an observer. To now, the majority of detected extragalactic VHE gamma-ray emitters belongs to the class of blazars. 
 
Most of such VHE gamma-ray emitters have been discovered win the last decade thanks to the operation of the current generation of IACTs represented by the MAGIC (Major Atmospheric Imaging Cherenkov) telescopes, H.E.S.S. (High Energy Stereoscopic System) and VERITAS (Very Energetic Radiation Imaging Telescope Array System). The numerous discoveries have been possible thanks to fundamental improvements in sensitivity and the extension of the energy range of these instruments with respect to their predecessors. In addition, the cooperation with instruments observing at other energies, for example in the optical regime and in the gamma-ray range below 100GeV, has emerged to be very important. 
 
Along the travel to Earth, the VHE gamma-ray emission of distant sources is attenuated due to the interaction with the extragalactic background light (EBL). 
This optical to infrared radiation is composed by the star light emission which is partially reprocessed by dust and continuously redshifted by the expansion of the Universe. Due to EBL absorption of VHE gamma-ray radiation, the intrinsic spectrum emitted by blazars is deformed. Such deformation scales with increasing energy of the VHE gamma-ray and with the source distance. For this reason, the AGNs detected in VHE gamma-rays are located at relative short distances. 
The most distant VHE gamma-ray emitter detected so far is the blazar 3C 279 located at redshift z = 0.536. 
 
This PhD thesis is focused on two research activities: a technical and a scientific part carried out within the MAGIC and CTA collaborations. The technical research is dedicated to the development of new IACT mirrors of improved optical performance and optimized price/performance ratio for future IACTs, while the scientific research concerns the detailed analysis of the VHE gamma-ray emission of two distant blazars, 1ES 0806+524 and 1ES 1011+496, observed with the MAGIC telescopes. 
 
The status of the development of new IACT mirrors for CTA is presented together with the optical qualifications of the first prototypes. In addition, a study of the reliability of such optical qualifications is reported. The observations of the VHE gamma-ray emission of 1ES 0806+524 and 1ES 1011+496 yield a detailed measure of the 
differential spectra which offer the possibility to probe the EBL. Finally, the MWL coverage allows a first precise SED determination.