Study of the divergent pointing mode for the Cherenkov Telescope Array Observatory Southern array

γ-rays are the most energetic among all electromagnetic radiation and provide us with a fascinating view of our universe under extreme conditions. Cherenkov telescopes represent one of the most efficient techniques for the ground based detection of γ-rays. The present generation of imaging atmospheric Cherenkov telescopes have taken γ-ray astronomy to an unprecedented level.The next generation of instruments for observing high-energy γ-rays is embodied by the Cherenkov Telescope Array Observatory (CTAO), which is currently under construction. More than 60 telescopes will be spread between two array sites in the Northern and Southern hemispheres, covering a wide range of energies from 20 GeV up to 300 TeV. Thanks to a sensitivity between 5 and 10 times greater than that of the current generation of instruments, CTAO will have unprecedented accuracy in high-energy γ-rays detection. While the properties of Cherenkov telescopes are optimal for the Very High Energy sky’s study, the time they need to achieve target sensitivity for the observation of large sky regions is really huge, due to their limited Field of View (FoV). To optimize the time spent to perform such tasks, a so-called divergent mode was proposed as an alternative observation strategy to the traditional - parallel - pointing. The idea that underlies this strategy is simple: an imaginary telescope, positioned at the center of gravity of the array, is pointed to a direction of interest, and all the telescopes are tilted outward from this direction. The single telescope pointing directions are computed thanks to a simple code that only requires one input parameter, called divergence (div). This strategy, while bringing the advantage of increasing the total instantaneous arrays’ FoV results in a worsening of the array performance. The goal of the studies performed on this topic is to find a balance between the FoV dimension and the array performance. Starting from 2013, when the strategy was first proposed, a few studies have been presented. Recently the Northern array performance was obtained in divergent mode. The simulations used for that study are based on an up-to-date simulation setup. The Southern site on the other hand was only simulated in older studies which were taking into account preliminary site and telescope (number and properties) definitions. This study aims at defining the Southern site performance in divergent mode for a set of configurations with different divergent setup applied. All classes of telescopes are considered and the most recent simulation configurations, for the telescope positions, cameras, optics, ecc, are used. Several scientific tasks can benefit from the enlarged FoV offered by this observation mode. Divergent pointing was part of a document stating CTA science requirements, as a strategy to perform extragalactic survey and a project referred to as transient survey. In recent years, with the first detection of Gravitational Wave events, the possibility to apply this strategy to look for electromagnetic counterparts of these objects has been opened. This thesis is organized as follows: Ch. 1: Introduction to γ-ray astronomy and ground based detection of γ-ray sources; Ch. 2: Imaging Atmospheric Cherenkov Technique and introduction the Cherenkov Telescope Array; Ch. 3: Introduction to the pointing modes alternative to the parallel one; Ch. 4: Description of the software needed for simulations and analysis; Ch. 5: Description of the Southern site simulations and analysis of the performance; Ch. 6: Analysis of the FoV evolution while tracking an object in divergent mode; Ch. 7: Open questions and possible alternative definitions of the divergent configuration. In addition, contributions to the LST collaboration are reported. This chapter is devoted to some cross-check analysis performed during the calibration of the LST-1 spare CaliBox and the data analysis performed during the Burst Advocate shifts.