Conditions for jet break-out in NS mergers

Maxim Lyutikov

doi:10.1093/mnras/stz3044

paper

Conditions for jet break-out in NS mergers

arXiv:1910.02769 · doi:10.1093/mnras/stz3044

Abstract

We consider conditions for jet break-out through ejecta following mergers of neutron stars and provide simple relations for the break out conditions. We demonstrate that: (i) break-out requires that the isotropic-equivalent jet energy $E_{j}$ exceeds the ejecta energy $E_{e j}$ by $E_{j} \geq E_{e j} / β_{0}$ , where $β_{0} = V_{e j} / c$ , $V_{e j}$ is the maximum velocity of the ejecta. If the central engine terminates before the break out, the shock approaches the edge of the ejecta slowly $\propto 1/ t$ ; late break out occurs only if at the termination moment the head of the jet was relatively close to the edge. (ii) If there is a substantial delay between the ejecta's and the jet's launching, the requirement on the jet power increases. (iii) The forward shock driven by the jet is mildly strong, with Mach number $M \approx 5/4$ (increasing with time delay $t_{d}$ ); (iii) the delay time $t_{d}$ between the ejecta and the jet's launching is important for $t_{d} > t_{0} = (3 / 16) c M_{e j} V_{e j} / L_{j} = 1.01 sec M_{e j, - 2} L_{j, 51}^{- 1} (β_{e j} / 0.3)$ , where $M_{e j}$ is ejecta mass, $L_{j}$ is the jet luminosity (isotropic equivalent). For small delays, $t_{0}$ is also an estimate of the break-out time.

Conditions for jet break-out in NS mergers

Abstract

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