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Electromagnetic signals from misaligned short Gamma-Ray Bursts in the dawn of gravitational wave astronomy

Published onJun 01, 2020
Electromagnetic signals from misaligned short Gamma-Ray Bursts in the dawn of gravitational wave astronomy

The joint detection of gravitational waves (GWs) and gamma-rays from a binary neutron star (NS) merger provided a unique view of off-axis gamma-ray bursts (GRBs) and an independent measurement of the NS merger rate. Comparing the observations of GRB170817 with those of the regular population of short GRBs (sGRBs), we show that an order unity fraction of NS mergers result in sGRB jets that breakout of the surrounding ejecta. We argue that the luminosity function of sGRBs is likely an intrinsic property of the sGRB central engine and that sGRB jets are typically narrow with opening angles of about 0.1 rad. We perform Monte Carlo simulations to examine models for the structure and efficiency of the prompt emission in off-axis sGRBs. The association with a kilonova provided unprecedented information regarding the physical properties of the different ejecta constituents. Combining this knowledge with the observed luminosities and durations of cosmological sGRBs detected by the Burst Alert Telescope (BAT) onboard the Neil Gehrels Swift Observatory, we revisit the breakout conditions of sGRB jets. We find that the time interval between the binary merger and the launching of a typical sGRB jet is less than about 0.1 s.

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