Ready, set, launch: time interval between BNS merger and short GRB jet formation

Understand

The joint detection of GW~170817/GRB 170817 confirmed the long-standing theory that binary neutron star mergers produce short gamma-ray burst (sGRB) jets that can successfully break out of the surrounding ejecta.

• At the same time, the association with a kilonova provided unprecedented information regarding the physical properties (such as masses and velocities) 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.
• Assuming self-collimation of sGRB jets does not play a critical role, we find that the time interval between the binary merger and the launching of a typical sGRB jet is $\lesssim0.1$~s.