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Re-solving the jet/cocoon riddle of the first gravitational wave with an electromagnetic counterpart
Giancarlo Ghirlanda (INAF - Osservatorio Astronomico di Brera)
Thursday 21/03/2019 @ 11:30, Sala IV piano Battiferro
The discovery of the electromagnetic emission associated with the gravitational wave event GW170817 posed several puzzling questions about its nature. While its thermal emission (the kilonova) was interpreted as the radioactive-decay heated expansion of the neutron rich ejecta launched by the merger, the non-thermal long lasting emission, peaking at ~200 days, raised several compelling questions about its nature. The simplest interpretation as a standard off—axis jet of a short Gamma Ray Burst was challenged by the power and temporal properties of the GW-EM signals. Alternative competing scenarios considered the possible presence of a failed (choked) jet producing a mildly relativistic nearly isotropic outflow. Only high resolution radio observations could resolve this puzzle showing that a relativistic jet emerged from the binary neutron star ejecta. I will present the evolution of the understanding of this still unique event and its implications.