Study of the Intergalactic Magnetic Field using LST-1 Data and Simulations within the CTAO Framework

The Cherenkov Telescope Array Observatory (CTAO) represents the next generation of ground-based observatories for very-high-energy (VHE; 20 GeV–300 TeV) gamma-ray astronomy. Its prototype system, LST-1, located at the Observatorio del Roque de los Muchachos (La Palma, Canary Islands), is currently in its commissioning phase and is already producing scientific-quality data. The main goal of this thesis is to investigate the intergalactic magnetic field (IGMF), a fundamental yet still poorly constrained component of the Universe, through its potential signatures in the spectra of distant extragalactic VHE gamma-ray sources. During their propagation over cosmological distances, gamma rays emitted by active galactic nuclei or gamma-ray bursts interact with the extragalactic background light, producing electron–positron pairs. These charged particles are deflected by the IGMF and subsequently generate secondary gamma rays through inverse Compton scattering, giving rise to a reprocessed emission component that may be detectable at VHE gamma rays. The IGMF therefore leaves characteristic imprints on the observed gamma-ray signal. Detecting and characterizing these signatures provides a powerful method for constraining the strength and structure of the IGMF using gamma-ray observations of blazars. The project is divided into two complementary parts. First, a spectral analysis of LST-1 observations of 1ES 1959+650 is performed as a case study to investigate the spectral modifications potentially induced by the IGMF. Second, a systematic phenomenological study is carried out to identify the most promising gamma-ray blazars for IGMF searches by combining CRPropa simulations with data analysis of sources from SteveCat and the current LST-1 observational sample. The resulting framework provides a quantitative method for assessing the detectability of IGMF signatures in any blazar. In particular, it will support source selection in the CTAO era, when the greatly improved sensitivity of the observatory is expected to significantly increase the number of detected VHE gamma-ray sources, enabling more stringent studies of the intergalactic magnetic field.