My research project will be focused on high energy astrophysics, dealing in particular with data analysis of the MAGIC telescope. The objects of my study will be a kind of very high energy γ-ray sources called Gamma-Ray Bursts (GRBs). I will be analyzing data of GRBs observed by MAGIC. The goals of this project are to investigate the mechanism that lead the very high energy emission of GRBs and to improve the sensitivity of their detections, also working on tools for future observations of these sources with the Cherenkov Telescope Array (CTA) experiment. Part of the project may will also concern with the connection between GRBs and sources of Gravitational Waves (GWs), through the alerts received by the experiment LIGO and, in the near future, by the experiment Virgo. The purpose is to find electromagnetic counterparts of the candidate events of GWs.
GRBs are powerful high-energy transient emission from sources at cosmological distances. They appear randomly on the celestial sphere and their emission is characterized by an initial short phase (~ hundred of seconds) of emission, called prompt emission, in hard-X rays and γ-rays, and a following phase of emission, called afterglow emission, with an emission peak energy shifted to longer wavelenghts ( X-rays, visible and radio) and that lasts from hours to weeks. The most approved scenario that try to explain the emission from GRBs is the internal/external shock scenario. This model predicts the existence of a central engine, a compact object like a black hole, that emits jets of non-thermal radiations. The highly variable gamma-ray emission characteristic of the GRB prompt phase is associated with the dissipation of the jet internal energy in midly relativistic shocks. The afterglow phase is associated with the jet deceleration where an external shock is formed by the interaction of the jet with the circum-burst medium. The progenitors of the central engine are related to the durations of prompt emission and so it is possibile to identify two distinct populations of GRBs:
- Long GRBs ( typical prompt emission durations > 2 s), believed to be produced by the collapse of massive star ( M > 15Mʘ)
- Short GRBs ( typical prompt emission durations < 2 s) may be connected to the merging of compact objects in binary systems.
The gravitational waves detectors such as Virgo or LIGO may help to investigate on the progenitors, especially for short GRBs.
The properties of the jets, the micro-physics, the progenitors and extra spectral component of very high energy emissions detect from GRBs are not so well known and understood and they opened several questions about GRB jet physics. The observation of these sources with ground-based telescopes is based on the imaging atmospheric Cherenkov tecnique. The main purpose of this technique is to combine spatial and temporal information of the measured Cherenkov light emitted to produce images of the showers and differentiate hadron and γ- initiated showers. MAGIC use this imaging technique to investigate the most powerful γ-ray sources of the celestial sphere. It is made by a stereoscopic system of two 17 m diameter Imaging Atmospheric Cherenkov Telescopes (IACTs) located on the Canary island of La Palma, in Spain. The system is specially designed to achieved the lowest possible energy threshold for this system and a fast response to transient phenomena. Observations of GRBs with MAGIC have always lead to upper limits on the flux emitted by these sources, due to their huge effective area and large photon statistics beyond 50-100 GeV. The future esperiment CTA will try to achieve low energy threshold ( ~ 10 GeV) to limit the absorption of high energy gamma rays from distant sources by the Extra-galactic Background Light ( EBL) and to improve the energy and angular resolution for a better background rejection. The telescopes designed to detect GRBs with CTA will be the Large Size Telescopes (LSTs), an array of four parabolic telescopes of 23 m diameter designed to be light- weighted to achieve fast repositioning to catch GRBs.
The goals of my research project will be:
- Investigate the high-energy properties of the GRBs, providing new constrains on GRB physics and useful information regarding their acceleration and emission processes at the highest energies
- Handle data analysis software of the MAGIC
- Study the connection between GRBs and GWs, searching for electromagnetic counterparts of GWs events collaborating with the experiment LIGO and Virgo.