Late-time accretion in neutron star mergers: implications for short gamma-ray bursts and kilonovae

Understand

We study the long-term (t >> 10 s) evolution of the accretion disk after a neutron star(NS)-NS or NS-black hole merger, taking into account the radioactive heating by r-process nuclei formed in the first few seconds.

• We find that the cumulative heating eventually exceeds the disk's binding energy at t ~ 10^2 s (\alpha/0.1)^{-1.8} (M/2.6 Msun)^{1.8} after the merger, where \alpha is the Shakura-Sunyaev viscosity parameter and M is the mass of the remnant object.
• This causes the disk to evaporate rapidly and the jet power to shut off.
• We propose that this is the cause of the steep flux decline at the end of the extended emission (EE) or X-ray plateau seen in many short gamma-ray bursts (GRBs).