Gamma-Rays and Multi-Messenger Signatures from Transient Phenomena
School
Universitat Autònoma de Barcelona - Institut de Física d'Altes Energies
External url: https://ddd.uab.cat/record/292605?ln=en
Abstract:
The cosmos is populated by astrophysical objects that can undergo once-in-a-lifetime transient astrophysical phenomena. In the most dramatic cases, the involved object can exhibit luminosities that surpass what our nearby Sun produces over its entire lifetime, in time spans of seconds. Observatories that detect various cosmic messengers, such as neutrinos and Gravitational Waves (GW), have opened up new possibilities to study these transient events in the framework of Multi-Messenger (MM) astronomy. The aim of the research conducted in this dissertation is to leverage open data streams and computational methods in order to facilitate the co-detection of cosmic messengers. When confronted with the MM approach, ground-based Imaging Atmospheric Cerenkov Telescope systems face certain obstacles. Working on a feasible strategy for the follow-up of MM alerts with the Major Atmospheric Gamma-ray Imaging Cherenkov Telescope (MAGIC) and the first deployed Large-Sized Telescope (LST-1), I adopted/elaborated a set of methodologies that allowed to implement tailored strategies for the generic small field of view instrument. The underlying algorithm culminated in an open-source software (ToOpy) and allows to execute time-critical follow-up observations on triggers from neutrino, GW, and Gamma-Ray Burst (GRB) alerts. Using ToOpy, real-time and archival data streams from observatories such as IceCube, Fermi, and LIGO-Virgo were accessed in order to isolate potential co-detections of multiple messengers. The proposal of ToOpy being valuable for this task was validated by recovering the spatio-temporal coincidences of the two major cornerstones of MM astronomy, namely TXS0506+056/IC-170922A as well as GRB170817A/GW170817. Along this line, ToOpy triggered follow-up observations of an IceCube TRACK alert by both the MAGIC and the LST-1 telescopes in March of 2021, but no excess very-high-energy gamma emission was recorded. Furthermore, ToOpy allowed to elaborate a catalog of host galaxies that serve as potential electromagnetic counterparts to CASCADE alerts issued by IceCube. Finally, digging through extensive GW event catalogs as well as GRB trigger data from Fermi-GBM, four unprecedented spatio-temporal coincidences were detected. While a bootstrapped approach lowers the significance of these novel associations, further study with Fermi-LAT data shows an interesting hint for an unrepeated (on a 10-year basis) high-energy gamma-ray flare from within the combined uncertainty region of the GRB and GW localization errors. On a different note, in the context of a Multi-Wavelength (MWL) study, I elaborate on my e↵orts to study the flaring TeV blazar VER J0521+211, which was observed by the MAGIC telescopes and other instruments during the spring of 2020. Leveraging therein extensive MWL coverage allowed to model the broadband spectral energy distribution by adopting time-evolving parameters for leptonic and leptohadronic emission mechanisms. Alongside these results, the combined gamma-ray spectra from MAGIC and Fermi-LAT allowed to constrain the unknown redshift for this particular blazar to a range of 0. 18 < z < 0. 243.