Principe, Giacomo (2015) Space and Time Clustering of High-Energy Photons detected by the Fermi-LAT. [Magistrali biennali]
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Since its launch in 2008, the Fermi -ray telescope has spent ~ 95% of its time in all-sky-survey mode, in which the Large Area Telescope (LAT) scans the entire sky every two orbits, or approximately every 3 hours (Atwood et al. 2009 ). For each detected event are recorded the informations on location, time and energy. They result in a large, multi-dimensional database which provides you a wealth of information about the -ray sky. The release of the new Fermi-LAT data, processed with the last Instru- ment Response Function (Pass8), has encouraged the Fermi collaboration to product new catalogs of sources at high energies. Among these catalogs there are the 3LAC (included in 3FGL catalog) and the 2FHL, both are objects of study and revision in my thesis. The method used to create these data set relied on wavelet-based algorithms. The source candidates were detected as uctuations above the background. These were then followed up with a full likelihood analysis. However, in the last two decades and over many disciplines, there has been a substantial amount of work on clustering analysis as a major statistical technique for classifying large data sets into meaningful subsets. In my thesis' work I developed and performed a clustering analysis to search new high energy sources. I chose to apply the clustering to the photons detected, between 50 GeV and 2 TeV, by the Fermi-Large Area Telescope (LAT) in 78 months of data. The possibility of increasing the known VHE -ray population of TeV- Cat2 active galactic nuclei (AGN) is attractive, particularly in the light of framing the scientifc priorities for the forthcoming Cherenkov Telescope Array (CTA; Actis et al. 2011 ). Chapter 1 presents the objective of my thesis and the importance of my analysis: the space and time clustering. Chapters 2 and 3 show the basics to understand the results presented in my thesis. Experienced readers in the field could skip them and go directly to the second part of the thesis. Chapter 2 provides an overview about the Fermi-LAT data analysis, which presents the -ray data and the analysis methods. Chapter 3 gives a general introduction, combined with main observed properties and interpretations, of AGNs.
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