Perspectives in multi-messenger astronomy: real-time follow-up to unravel gamma-ray counterparts from neutrino alerts with Cherenkov Telescope Array Observatory

This thesis investigates the prospects for multi-messenger astrophysics with next-generation observatories, specifically focusing on the real-time identification of veryhigh-energy (VHE) gamma-ray counterparts to astrophysical neutrino alerts. Thecore of the work consists of evaluating the detection capabilities of the futureCherenkov Telescope Array Observatory (CTAO) through extensive simulations. Us-ing the FIRESONG framework, I modeled populations of extragalactic neutrino sources,including both steady-state emitters and transient flares similar to TXS 0506+056. Ideveloped an original analysis chain implementing the Gammapy framework to assessthe detectability of these sources, demonstrating a significant observational synergybetween KM3NeT/ARCA and CTAO-South.To bridge the gap toward operational readiness, I performed a technical validationof the "Transient Handler" for the LST-1 telescope. By analyzing system latency andperformance, I ensured its capability to handle external triggers for rapidly fadingtransients. Finally, the developed pipeline was applied to real LST-1 data fromTarget-of-Opportunity campaigns on the sources PKS 1424+240 and VER J0521+211.While no significant gamma-ray excess was found, I derived 95% C.L. upper limitsthat provide critical constraints on hadronic emission models. This work demonstratesthat the combination of CTAO’s sensitivity and optimized real-time strategies willbe fundamental for identifying the cosmic accelerators of the non-thermal Universe