PRIN: PROGETTI DI RICERCA DI RILEVANTE INTERESSE NAZIONALE

PEACE: Particle Emission and Acceleration in the most powerful Cosmic Explosions

Project description

Gamma-ray bursts (GRB) are natural candidates to shed light on extreme phenomena such as the formation and properties of relativistic outflows, particle acceleration in relativistic plasmas, and the birth of compact objects from the core-collapse of massive stars (long GRBs) or from the merger of neutron stars/black holes (short GRBs) associated with the generation of gravitational waves (GW). Despite there is a general grasp on how GRB radiation is produced, open questions and inconsistencies between model predictions and observations are preventing us from fully exploiting these sources.

Recently, Imaging Atmospheric Cherenkov Telescopes (IACT) detected TeV emission from four GRBs, proving for the first time that GRBs can be sources of very-high energy (VHE) emission. This discovery completely changes the expectations on performing GRB science with the Cherenkov Telescope Array (CTA), the next generation of Cherenkov telescopes, for which GRBs have now become one of the main targets. Despite the small number of detections, the new observational window is already providing us with fruitful, complementary information: theoretical efforts are now needed to exploit current and upcoming data to concretely advance our understanding of GRBs. The advent of CTA makes the topic extremely timely and urgent.

In this proposal, we plan to model GRB radiation, and in particular HE (0.1-100 GeV) and VHE (>100 GeV) data, with the main aim of constraining the processes occurring in relativistic plasmas.

We recently found convincing evidence that GRB prompt emission is synchrotron from electrons undergoing incomplete cooling. We propose to couple this new information with calculations of the associated synchrotron self-Compton (SSC) component and dedicated analysis of simultaneous (V)HE observations, to constrain the physical parameters describing the emission region (magnetic field, bulk Lorentz factor, distance from the central engine, number and energy of the accelerated particles) and in turn the properties of the outflow.

For afterglow radiation, we plan to focus on GRBs with photon energies >10GeV and model their multiwavelength radiation to specifically constrain particle acceleration (efficiency, maximum electron energy, and magnetic field generation). Interestingly, a hint of afterglow TeV emission has been found also in a short GRB, but the inferred TeV flux is too large to be explained by a one-zone SSC model. A possibility to explain an enhanced inverse Compton (IC) emission is to consider a jet with an angular-dependent velocity. Such a jet structure is more realistic and is also the one required by the modeling of the short GRB170817 associated with a GW detection. Hence, we propose to develop proper calculations of VHE IC radiation taking the effects of such a structure into account. The study is extremely relevant for future observations of TeV counterparts to GW events.

Members

Research Unit 1: INAF - Osservatorio Astronomico di Brera (Merate, LC, Italy)

• PI: Dr. Lara Nava

• Co-Is: Dr. Giancarlo Ghirlanda, Dr. Om Sharan Salafia

• Postdocs: Dr. Gustavo Soares

Research Unit 2: SISSA - Scuola Internazionale Superiore di Studi Avanzati (Trieste, TS, Italy)

• PI: Prof. Annalisa Celotti

• Co-Is: Prof. Francesco Longo

• Postdocs: Dr. Zhi-Qiu Huang

Codice progetto: 202298J7KT - PEACE

CUP INAF: C53D23000960006

CUP SISSA: G53D2300088 0006