Multifrequency Data from Active Galactic Nuclei

There is growing interest from the Astrophysics community to identify and study gamma-ray sources, especially the ones detected at E>100GeV in the Very High Energy (VHE) regime. Distant galaxies harboring an Active Nucleus (AGN) were recently detected as major extragalactic sources of TeV photons, turning to be key component for a variety of studies like understanding AGN's jet properties and composition, or probing emission mechanism probably in the vicinity of super massive black holes (SMBH). Even more remarkable are the multitude of questions currently being addressed by considering the interaction of VHE photons along its propagation through cosmological distances, such as unveiling the spectral shape of the Extragalactic Background Light (EBL), probing the existence of Intergalactic Magnetic Fields, or even addressing fundamental question related to Quantum Gravity and Stand Model physics. So far, the number of such VHE "Astrophysical laboratories" identified up to now is not that big, reaching only 148 galactic/extragalactic TeV detected sources. This work took forward the idea of preparing a large catalog of High Synchrotron Peak blazars (HSP), which shows to be the most abundant population of extragalactic TeV emitters, with the main goal of revealing and characterize promising targets for TeV observatories. HSP blazars are remarkably rare, with only a few hundreds of them expected to be above the sensitivity limits of currently available surveys. To find these very uncommon objects, there was devised a method that combines multifrequency selection criteria based in unique features from HSP's Spectral Energy Distribution. The so called 1WHSP sample was assembled including ~1000 sources that were characterized case by case, and since it is the largest sample of HSP blazars, a series of population studies were performed. The reliability of using the 1WHSP sample for unveiling gamma-ray emitters was confirmed, since it allowed to associated many newly identified sources from the 3FGL catalog with their 1WHSP counterparts. Also, by performing gamma-ray data analysis in the energy range 300MeV-200GeV, based on six year of observations with Fermi satellite and making use of the Fermi Science Tools, a dozen of new gamma-ray point-like sources were unveiled. Considering multifrequency data from radio to gamma-rays, a list with the 22 brightest 1WHSP sources was studied in details, and its potential for detectability with H.E.S.S.II observatory was evaluated. By properly extrapolating the measured gamma-ray spectrum to higher energies, and taking into account the absorption of VHE photons due to interaction with EBL light, the observation time need for a significant detection was estimated, and is part of a recent TeV observation proposal submitted to the HESS observatory (see appendix). Still, there is a large potential for expanding the present catalog, and it has already brought significant information for the VHE Astrophysics community, since before this work there was no clear estimation for the number of sources that could be in reach of the present and upcoming generation of VHE observatories like the Cherenkov Telescope Array (CTA). In addition, by correlating the arrival direction of ultra high energy cosmic rays (UHECR) with the position of bright 1WHSP sources, it is shown that HSP blazars could well be part of the population emitting UHE particles. Such result is unique in the sense that it is based on direct source-event chance associations, and particularly interesting since it challenges what was previously expected for direct associations of this kind. In brief, the interaction of UHECR with background photons would attenuate sources further than 100Mpc (known as GZK horizon), instead the associated 1WHSP sources extends at least up to z=0.4 meaning one order of magnitude larger distance.