Neutron-Star Formation, Thermonuclear Supernovae, and Heavy-Element Reimplosion

The reimplosion mass fraction of a presumed supernova explosion is calculated under the assumption of the dynamical formation of a remnant neutron star. It has been pointed out by Arnett and Truran that previous numerical calculations of supernovae based upon transport of heat by neutrinos and dynamical neutron-star formation predicted the ejection of inconsistently large (X 10 ) amounts of neutron-rich matter. The present analytical calculations of the behavior of matter adjacent to the neutron star immediately after the explosion show that this matter cools so rapidly by neutrino emission that reimplosion occurs and a rarefaction wave progresses outward from the surface of the neutron star and reverses the radial trajectory of matter previously exploding. When the rarefaction overtakes exploding matter whose velocity is significantly greater than escape velocity, escape continues. For a rather wide range of explosion conditions (adiabat and surface velocity), an inner mass fraction of 50 percent of the initially expelled matter reimplodes and removes essentially all the neutron-rich matter from further observation. The subsequent continuing and small reimplosion luminosity is calculated; at late times (106 seconds) it is shown to be small, 2.2 X 1038 ergs , and to have a decay time of 5 X 10 seconds.