Spherically symmetric simulation with Boltzmann neutrino transport of core collapse and postbounce evolution of a 15 M⊙ star

We present a spherically symmetric, Newtonian core collapse simulation of a 15 M-circle dot star with a 1.28 M-circle dot iron core. The time-, energy-, and angle-dependent transport of electron neutrinos (nu(e)) and antineutrinos (<(nu)over bar>(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(nu/c) in the velocity nu of the stellar medium. The supernova shock expands to a maximum radius of 350 km instead of only similar to 240 km as in a comparable calculation with multigroup flux-limited diffusion (MGFLD) by Bruenn, Mezzacappa, & Dineva. This may be explained by stronger neutrino hearing 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 similar to 170 hm 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-circle dot 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 Y-e> 0.5 in the neutrino-heated matter, which suggests that the overproduction problem of neutron-rich nuclei with mass numbers A approximate to 90 in exploding models may be absent when a Boltzmann solver is used for the nu(e) and <(nu)over bar>(e) transport.