Origin of the Binary Pulsar J0737-3039B

Evolutionary scenarios suggest that the progenitor of the new binary pulsar J0737-3039B was a He star with $M>(2.1--2.3){\mathrm{M}}_{\ensuremath{\bigodot}}$. We show that this case implies that the binary must have a large ($>120\text{ }\text{ }\mathrm{k}\mathrm{m}/\mathrm{s}$) center of mass velocity. However, the location, $\ensuremath{\sim}50\text{ }\mathrm{p}\mathrm{c}$ from the Galactic plane, suggests that the system has, at high likelihood, a significantly smaller center of mass velocity and a progenitor more massive than $2.1{\mathrm{M}}_{\ensuremath{\bigodot}}$ is ruled out (at 97% C.L.). A progenitor mass around $1.45{\mathrm{M}}_{\ensuremath{\bigodot}}$, involving a new previously unseen gravitational collapse, is kinematically favored. The low mass progenitor is consistent with the recent scintillation based velocity measurement of $66\ifmmode\pm\else\textpm\fi{}15\text{ }\text{ }\mathrm{k}\mathrm{m}/\mathrm{s}$ and rules out the high mass solution at 99% C.L. Conversely, if the unlikely higher mass solution is the true one we should increase the estimated rate of neutron star mergers by a factor of at least 2.

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