http://arxiv.org/abs/1910.02769
We consider conditions for jet break-out through ejecta following mergers of neutron stars. We demonstrate that: (i) break-out requires that the jet energy $E_j$ exceeds the ejecta energy $E_{ej}$ by $E_j \geq E_{ej}/ \beta_0$, where $ \beta_0 = V_0/c$, $V_0$ 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 $t_d >t_0= ({3 }/{16} ) {c M_{ej} V_0}/{L_j} = 1.01 {\rm sec} M_{ej, -2} L_{j, 51} ^{-1} \left ( {\beta_w} /{0.3} \right)$, where $M_{ej}$ 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.
M. Lyutikov
Tue, 8 Oct 19
74/88
Comments: N/A
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