Archival search of very high energy transient sources with the MAGIC telescopes
School
Universitat Autònoma de Barcelona - Institut de Física d'Altes Energies
Abstract:
Transient sources are astronomical objects or events that evolve in short timescales (from milliseconds to days). The transient sky in Very High Energy (VHE) gamma-rays offers a window into the most energetic and dynamic processes in the Universe. This thesis introduces a novel algorithm for the archival search of transient VHE sources with the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes, a system of two Imaging Atmospheric Cherenkov Telescopes (IACTs). After 20 years in operation, the MAGIC telescopes have accumulated vast amounts of observational data, but the day-to-day observation of transients depends on alerts from other experiments. This new method aims to leverage archival data for the search of transient events. The method is designed as an unbiased direct search for transients with no a-priori assumptions on their temporal or spectral profiles, with its main parameter being the timescale of the target source. We applied the search in four different timescales, 2 s, 10 s, 100 s and 1000 s, and focused the analysis of the results on the case of Primordial Black Hole (PBH) evaporation. PBHs are hypothesized to have formed in the early Universe due to density fluctuations and have a wide range of possible initial masses. PBHs with an initial mass around 10 11 − 10 12 kg are an attractive target for IACTs, since they would be reaching the end of their lifetimes today with an intense and fast explosion of VHE particles due to Hawking radiation. A detection of VHE emission from PBHs would, in addition to confirming their existence, constitute the first proof for Hawking radiation and have a wide impact on cosmological models. Focused on the detection of PBH evaporation, this work presents an analysis of one year of observational archival data from MAGIC. While several candidate signals emerged in our search, none had enough statistical significance to warrant a detection claim for PBH evaporation or other transient event. Nevertheless, the non-detections yielded upper limits on the evaporation rate density of PBHs near Earth in previously unexamined parameter space. These results were used to discuss the different approaches to observing PBHs used by MAGIC and other gamma-ray experiments, and derive upper limits on the PBH density ratio in the early Universe. Additionally, we obtained generic upper limits on the number of transient flares per year as a function of their integrated flux, for different spectral assumptions. The development of a background estimation model as part of this thesis improves our capability to analyse vast datasets for the search of transient events. The algorithms and methodologies developed herein can be used in future searches focused on different transient events, or applied to a larger dataset. This thesis contributes to setting new upper limits in the field but also advances the analytical tools available for future transient searches in the VHE domain.