Radio exploration of the transient sky: Binary mergers and peculiar core-collapse supernovae



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Astrophysical transients are a class of variable sources often associated with some of the most cataclysmic phenomena in the universe, such as compact object (neutron stars and black holes) mergers and explosions of massive stars. Observations over the last few decades have shown that the radio sky is very dynamic on short timescales. Radio studies of transients uniquely unveil key information on the physics at play in these events, as well as important clues on the properties of their surroundings. For example, radio observations of extreme transients are an effective tool to probe particle acceleration in relativistic shocks; characterize the properties (such as speed and energy) of their ejecta; study the mass loss history of pre-supernova progenitors; constrain the density of the insterstellar medium (ISM) in which fast ejecta expand and/or the structure and density of the circumstellar environment; distinguish engine-powered relativistic transients from non-relativistic ones powered by strong circumstellar interaction; and provide hints on the equation of state of neutron stars. Hence, radio observations bring us a complementary view of the transient universe to that obtained through observations at other wavelengths of the electromagnetic spectrum, or via other messengers (such as gravitational waves). This thesis focuses on the detailed study of a few radio transients that are related to the birth of compact objects, either via the merger of other compact objects in binary systems, or via massive star explosions. Specifically, I focus on: (i) GW170817, the first binary neutron star merger to be observed in both gravitational waves and electromagnetic waves, and the late-time search for a kilonova radio afterglow as a tool to characterize the nature of the compact object left over after the merger; (ii) Radio follow-up observations of candidate binary neutron stars mergers identified during the latest observing run of ground-based gravitational wave detectors; (iii) SN,2004dk, a stripped-envelope core-collapse supernova representative of the class of radio-loud massive star explosions in which radio observations can disentangle relativistic ejecta powered by a compact object engine, from non-relativistic strong circumstellar interaction related to the pre-supernova progenitor mass loss history.

Embargo status: Restricted until 09/2023. To request the author grant access, click on the PDF link to the left.



Radio Transients, EMGW, GW170817, Kilonova Afterglow, SN2004dk, Type Ib Supernovae