MAGIC telescopes observations at Very Large Zenith angles and the first neutrino-gamma association

Questa tesi di dottorato riassume le mie attività nell'ambito dell'esperimento MAGIC. Il lavoro è incasellato nell'ambito dei raggi cosmici e in particolare alle componenti galattica ed extragalattica. La tesi apre con una introduzione all'argomento e all'importanza di messaggeri neutri come fotoni e neutrini. Prosegue descrivendo le principali caratteristiche e i principali sottosistemi dei telescopi MAGIC rilevanti per questa ricerca. La tesi descrive due argomenti principali a cui ho contribuito. Il primo riguarda l'applicazione di una nuova tecnica nell'ambito di telescopi Cherenkov: osservazioni a grandi angoli zenitali. Tale tecnica permette di accrescere l'area efficace dello strumento e la sue energia di soglia. Questo potrà permettere di investigare la componente galattica dei raggi cosmici ad energie oltre i 100 Tera (10^12) elettronvolt. La tesi descrive inoltre il mio contributo alla detenzione della prima sorgente astrofisica extragalattica da cui si abbia rilevato in coincidenza spaziale un neutrino ad alta energia misurato dall'esperimento IceCube. La tesi conclude enfatizzando i risultati ottenuti, il loro peso nel futuro dei raggi cosmici e il confronto con strumenti di nuova generazione.

This PhD thesis summarises research activities I carried out as a member of the MAGIC collaboration (https://magic.mpp.mpg.de). My work belongs to the field of cosmic rays, for which lack of knowledge about their origin and nature of their energy spectrum represents one of the major open problems in modern astrophysics. This research deals with both galactic and extragalactic sources. The thesis opens with an introduction to cosmic rays, and on the importance of using neutrally charged messengers like photons and neutrinos to probe the presence of cosmic rays at the sites of cosmic acceleration. It continues by describing the general structure and performance of the MAGIC telescopes, in particular the subsystems and data analysis steps relevant to the subjects reported in this thesis. It then explains the importance of a novel observational technique pioneered by MAGIC, which constitutes one of the two original activities on which I have contributed. The research conducted on this subject consists in laying down the development and optimisation of the data analysis techniques in order to allow the MAGIC telescopes to operate at Very Large Zenith Angle (VLZA) observations - i.e. towards the horizon. This will possibly allow the first detection of Very High Energies (VHE) sources by an experiment such as MAGIC, not only in the multi TeV ( TeV = tera electron Volts = 1012eV ) range but also at higher energies, up to ∼ 100TeV where the nature of the observed emission can give insights on the possibility of cosmic ray acceleration in - situ. The second part of the thesis describes a major scientific breakthrough for MAGIC and for the whole astrophysical community. In 2017 an alert from the IceCube experiment triggered a response from MAGIC as well as a number of different satellites and ground observatories worldwide. For the first time a VHE photon coincident with a VHE neutrino has been detected. This caused the entire community to focus on a source that was later identified as a blazar (an Active Galactic Nucleus whose relativistic jet points at the observer). The fourth chapter illustrates my contribution to the MAGIC data analysis which led to the VHE γ-ray detection of the neutrino source. The conclusions emphasise the importance of investigations from the point of view of current cosmic ray physics and future research in the field.