In recent years the transient sky astronomy has made great strides, propelled by the progress of state-of-the-art technology. Relativistic explosions and their progenitors, such as gamma-ray bursts (GRBs) and relativistic supernovae (SNe), are the focus of forefront research and can be studied not only over a broader range of the electromagnetic spectrum, but also through high-energy neutrinos and gravitational waves (GWs). GRB afterglows --broadband long-lasting emissions originating from the interaction between the relativistic ejecta and the circumburst medium-- are crucial to examine many open issues, such as relativistic shock microphysics, energetics, the jet structure, and the magnetization of the ejecta. All these issues are ideally constrained through observations at radio frequencies, which are however hampered by the typical faintness (mJy or sub-mJy) of the sources, resulting in a 30% of detection rate. Except for a couple of ambiguous cases, long GRBs are found to be associated with type Ic broad-lined supernovae (Ic-BL SNe), detected --with current facilities-- at redshift z < 1. In general, only a fraction of Ic-BL SNe harbours a relativistic jet detectable as a GRB. There are different altenative interpretations: (i) true absence of any GRB jet, (ii) the presence of a GRB jet, whose axis is off our line of sight though (“off-axis scenario”) (iii) the jet fails to make it out to the progenitor’s photosphere (“chocked jet scenario”). In this talk I will discuss the broadband modelling of relativistic explosions, and how the Sardinia Radio Telescope can effectively contribute to the field.
 

Breve CV di Marco Marongiu:

Marco Marongiu was born in Iglesias, Sardinia, and he graduated in Physics at the Cagliari University in 2013, with a master thesis about the simulation of observations of pulsars with the Sardinia Radio Telescope (SRT). After graduation, he continued to collaborate with Cagliari Astronomical Observatory in the first SRT early science proposals, mostly concerning the imaging analysis of Supernovae Renmants. After being a teacher of Mathematics and Physics in the high schools for two years, in 2016 he won a Ph.D. position at Ferrara University and he studied the broadband modelling of relativistic explosions, such as Gamma-Ray Bursts and their connection with Supernovae. He supervised a proposal and two ToO to observe GRB afterglows with SRT, in order to better understand the emission of these sources at low frequencies. He collaborates with several groups of research to analyse and reduce the radio data (ATCA, VLA) from GRB afterglows and Supernovae.