Spherically Symmetric Simulation with Boltzmann Neutrino Transport of Core Collapse and Postbounce Evolution of a 15 [ITAL]M[/ITAL][TINF]⊙[/TINF] Star

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Abstract
We present a spherically symmetric, Newtonian core collapse simulation of a 15 M☉ star with a 1.28 M☉ iron core. The time-, energy-, and angle-dependent transport of electron neutrinos (νe) and antineutrinos (e) was treated with a new code that iteratively solves the Boltzmann equation and the equations for neutrino number, energy, and momentum to order O(v/c) in the velocity v of the stellar medium. The supernova shock expands to a maximum radius of 350 km instead of only ~240 km as in a comparable calculation with multigroup flux-limited diffusion (MGFLD) by Bruenn, Mezzacappa, & Dineva. This may be explained by stronger neutrino heating due to the more accurate transport in our model. Nevertheless, after 180 ms of expansion the shock finally recedes to a radius around 250 km (compared to ~170 km in the MGFLD run). The effect of an accurate neutrino transport is helpful but not large enough to cause an explosion of the considered 15 M☉ star. Therefore, postshock convection and/or an enhancement of the core neutrino luminosity by convection or reduced neutrino opacities in the neutron star seem necessary for neutrino-driven explosions of such stars. We find an electron fraction Ye > 0.5 in the neutrino-heated matter, which suggests that the overproduction problem of neutron-rich nuclei with mass numbers A ≈ 90 in exploding models may be absent when a Boltzmann solver is used for the νe and e transport.