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Si us plau utilitzeu sempre aquest identificador per citar o enllaçar aquest document: https://hdl.handle.net/2445/224273
Transient sources with LST-1: study of novae, supernovae, and gamma-ray bursts
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[eng] The branch of astrophysics that studies transient phenomena allows the exploration of astronomical sources that show temporal variability that can extend from a few fractions of a second to scales as long as tens of years. These transient events can give rise to a wide variety of phenomena observed throughout the electromagnetic spectrum. In some cases, these events may even be associated with the detection of gravitational waves or the emission of neutrinos. The detection of transient and highly energetic electromagnetic emission in the gamma-ray range (with energies above 100 MeV) is usually related to drastic changes in the environment of the system that emits this radiation. In some cases, these transitory phenomena can be produced due to their partial or total destruction. During these episodes, the source can become extremely luminous, becoming one of the brightest in the sky, even if it is located at cosmological distances. Despite advances in this field of research in recent years, the mechanisms that produce the emission of gamma rays from transient sources remain enigmatic, regardless of the nature of the source that produces them. Gamma rays in the energy range from tens of GeV to hundreds of TeV can be detected from the ground with Cherenkov telescopes. This Thesis is framed precisely in the study of transient sources using the first prototype of the new generation of Cherenkov telescopes, which will be part of the future Cherenkov Telescope Array Observatory (CTAO). The CTAO will be made up of different types of telescopes distributed over a large area, forming an array of Cherenkov telescopes in order to detect gamma rays in a wide range of energies. CTAO's largest telescopes, called Large-Sized Telescopes (LSTs), are optimized to detect relatively low-energy gamma rays of a few tens of GeV. The first of these telescopes (LST-1) is in the commissioning phase, although at the same time it is already beginning to give the first scientific results. In addition, there are currently three LSTs under construction. This thesis focuses on the study of transient sources in the range of very high energy gamma rays (100 GeV < E < 100 TeV). A detailed study of nova and supernova explosions (SNe) and gamma-ray bursts (GRBs) has been carried out. We studied the emission produced in the RS Ophiuchi source, the first nova explosion ever detected in the very high energy range. We analyzed data obtained concurrently with LST-1 and the Fermi-LAT telescope during this event. We have modeled its emission using the most complete gamma-ray spectrum ever obtained by an event of these characteristics, which includes in addition to the observations taken with LST1 and Fermi-LAT, the data obtained with the Cherenkov MAGIC and H.E.S.S. telescopes. We have also evaluated the prospects for future detections of new explosions with the CTAO, highlighting the excellent capabilities of LSTs to detect this type of event and restricting the relevant physical parameters involved in gamma-ray emission. We searched for very high-energy gamma-ray emission in two nearby supernovae produced during the collapse of a very massive star, labeled SN 2023ixf and SN 2024bch. These supernova explosions were observed with LST-1 and the MAGIC telescopes a few weeks after their discovery. Although neither of the two sources has been detected, we have been able to obtain upper limits to their possible flow of very high-energy gamma rays, emphasizing the strengths and limitations that observations in this range can offer for the understanding of the physical phenomena that give rise to this type of explosion. We studied the very high-energy gamma-ray emission of GRB 221009A, known as the brightest GRB of all time. Observations obtained with LST-1 show an excess of gamma rays with a statistical significance of 4.1σ during the first observations. We have restricted its emission of very high-energy gamma rays and compared it with several theoretical models that can consistently explain the multi-wavelength data obtained with different telescopes for this event. Our results can help resolve the current degeneration between some of these theoretical models compatible with the broadband emission of this event. The results obtained by these three types of sources highlight the excellent capabilities of LSTs for the study of transient gamma-ray sources. In addition, these results provide a first taste of the potential of CTAO to study these types of events.
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AGUASCA I CABOT, Arnau. Transient sources with LST-1: study of novae, supernovae, and gamma-ray bursts. [consulta: 2 de desembre de 2025]. [Disponible a: https://hdl.handle.net/2445/224273]