Gamma-ray bursts are powerful flashes of high-energy photons that happen randomly in the sky with a frequency of ~2 per day. They are usually divided in two families on the basis of their duration: short (lasting less than 2 s) and long. Long GRBs are linked with the death of massive stars and are detected up to very high redshift. Short GRBs are now firmly linked to the merger of two neutron stars and connected with the emission of gravitational waves.
INTEGRAL/IBAS GRBs. Our institute involvement in the GRB field started with the realization of the INTEGRAL Burst Alert System (IBAS) and is now continuing with the study of afterglows with XMM-Newton and Swift. IBAS has been developed under the IASF-Milano responsibility as part of the Italian contribution to the INTEGRAL Science Data Center (ISDC). IBAS is a software system, running on ground at the ISDC, to detect and localize in near real time the GRBs detected by the INTEGRAL instruments. In particular, the GRBs in the IBIS field of view can be localized with an uncertainty of 2 arcmin and their positions distributed within a few seconds. IBAS started to operate immediately after the INTEGRAL launch at the end of 2002, providing the first rapid and accurate localizations at a rate of about one GRB/month. IASF scientists are currently responsible for the maintenance and operations of IBAS, in collaboration with the ISDC, and for the quick look interactive analysis performed after the automatic alerts delivery in order to validate the events, derive refined information and distribute the GCN notices. Besides studying the GRB prompt emission with INTEGRAL data, we have also been active in the observations of GRB afterglows, mainly exploiting our expertise with the XMM-Newton EPIC instrument, but also using Swift XRT data.
Follow-up of GW events. The detection of GW170817/GRB170817A opens the so-called multi-messeger era, in which gravitational waves are coupled with electro-magnetic information to provide a complete picture of astrophysical phenomena. We are involved in the search of the electro-magnetic counterpart of GW event both using space facilities (INTEGRAL, Agile, Fermi) and ground-based telescope being part of the GRAWITA and ENGRAVE collaborations.
Statistical study of the GRB population. Complete samples are at the base of any population studies. We are now studying the rest-frame properties of well-selected complete sub-samples of long and short GRBs detected by Swift. For the first time, our complete samples allow us to study in an unbiased way the properties of long and short GRBs and their evolution with cosmic time. They also provide a critical test for population synthesis models aimed to make reliable prediction for future GRB missions. In particular, we are involved in compute the expected rate of GRB detections for the THESEUS satellite (for both the SXI and XGIS instruments).
GRB host galaxies. We are studying a complete sample of long GRB host galaxies. By comparing the GRB host properties, i.e. stellar mass, star-formation rate and metallicities, with those of star-forming field galaxies detected in dedicated survey we will be able to better understand where GRBs form and constrain the nature of the GRB progenitors.
Galactic dust studies with GRB afterglows. A line of activity consists in the study of X-ray scattering rings observed around GRBs. These are produced by dust layers in our Galaxy and provide a mean to derive extremely accurate distances for the dust clouds, and in some cases also to constrain the properties of the prompt GRB emission at soft X-ray energy. We have developed a sensitive method to optimize the detection and study of faint dust scattering expanding rings.