Broadband Modeling of Relativistic Explosions

In recent years, transient sky astronomy has made great strides, driven by advancements in state-of-the-art technology. Relativistic explosions and their progenitors, such as gamma-ray bursts (GRBs) and relativistic supernovae (SNe), are at the forefront of research and can be studied not only across 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 for examining many unresolved issues, such as relativistic shock microphysics, energetics, 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% 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 harbors a relativistic jet detectable as a GRB. There are different alternative interpretations: (i) true absence of any GRB jet, (ii) the presence of a GRB jet, whose axis is off our line of sight (“off-axis scenario”), (iii) the jet fails to make it out to the progenitor’s photosphere (“choked jet scenario”). In this talk, I will discuss the broadband modeling of relativistic explosions and how the Sardinia Radio Telescope can effectively contribute to the field.

Brief CV of Marco Marongiu:

Marco Marongiu was born in Iglesias, Sardinia, and graduated in Physics at the University of Cagliari in 2013, with a master’s thesis on the simulation of pulsar observations with the Sardinia Radio Telescope (SRT). After graduation, he continued to collaborate with the Cagliari Astronomical Observatory on the first SRT early science proposals, mostly concerning the imaging analysis of Supernova Remnants. After teaching Mathematics and Physics in high schools for two years, in 2016 he won a Ph.D. position at the University of Ferrara, where he studied the broadband modeling 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, to better understand the emission of these sources at low frequencies. He collaborates with several research groups to analyze and reduce radio data (ATCA, VLA) from GRB afterglows and Supernovae.