The extremes of the Fermi-LAT energy ranges: the Fermi Low Energy (1FLE) catalog and a detailed investigation of HESS J1825-137 above 100 GeV

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Doctoral Thesis
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Principe, Giacomo

In the last decades, important improvements have been made in the gamma-ray astronomy. Thanks to the fact that photons travel in straight lines it is possible to search and localize the sites where gamma rays are produced in the Universe. Several gamma-ray point-source analyses have been performed by space- and ground-based telescopes in the MeV to TeV energies. In particular, the imaging Compton telescope (COMPTEL) onboard NASA's Compton Gamma-Ray Observatory detected sources below 30 MeV, while catalogs of point sources released by the Fermi Large Area Telescope (LAT) and EGRET collaborations use energies above 100 MeV. Because the Fermi LAT is able to detect gamma rays with energies as low as 20 MeV, a catalog of gamma-ray sources detected in the energy range between 30 and 100 MeV is presented in this work for the first time. This catalog closes the gap of point source analysis between the COMPTEL catalog and the Fermi-LAT catalogs. The first part of this work contains the details of the analysis and results of the first catalog of gamma-ray sources detected between 30 and 100 MeV with Fermi LAT.

Subsequently, a detailed study of the evolution of the pulsar wind nebula (PWN) HESS J1825-137 is presented. PWNe are archetypal celestial sources, in which it is possible to test the theoretical models for the particle acceleration mechanisms. The analysis of the HESS J1825-137 has been performed using 10 years of Fermi-LAT data between 1 GeV and 1 TeV.

The second part of this work focuses on the characterization and performance verification of the photon detectors planes (PDPs) for the camera of the medium-sized telescopes of the Cherenkov Telescope Array (CTA), which is the next generation ground-based observatory for gamma-ray astronomy at very-high energies.

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