Two-dimensional hydrodynamic core-collapse supernova simulations with spectral neutrino transport - II. Models for different progenitor stars

Spherically symmetric (1D) and two-dimensional (2D) supernova simulations for progenitor stars between 11M(circle dot) and 25M(circle dot) are presented, making use of the PROMETHUS/VERTEX neutrino-hydrodynamics code, which employs a full spectral treatment of neutrino transport and neutrino-matter interactions with a variable Eddington factor closure of the O(upsilon/c) moments equations of neutrino number, energy, and momentum. Multi-dimensional transport aspects are treated by the ray-by-ray plus approximation described in Paper I. We discuss in detail the variation of the supernova evolution with the progenitor models, including one calculation for a 15 M-circle dot progenitor whose iron core is assumed to rotate rigidly with an angular frequency of 0.5 rad s(-1) before collapse. We also test the sensitivity of our 2D calculations to the angular grid resolution, the lateral wedge size of the computational domain, and to the perturbations which seed convective instabilities in the post-bounce core. In particular, we do not find any important differences depending on whether random perturbations are included already during core collapse or whether such perturbations are imposed on a 1D collapse model shortly after core bounce. Convection below the neutrinosphere sets in 30-40 ms after bounce at a density well above 10(12) g cm(-3) in all 2D models, and encompasses a layer of growing mass as time goes on. It leads to a more extended proto-neutron star structure with reduced mean energies of the radiated neutrinos, but accelerated lepton number and energy loss and significantly higher muon and tau neutrino luminosities at times later than about 100 ms after bounce. While convection inside the nascent neutron star turns out to be insensitive to our variations of the angular cell and grid size, the convective activity in the neutrino-heated postshock layer gains more strength in better resolved models. We find that low (l = 1, 2) convective modes, which require the use of a full 180 degree grid and are excluded in simulations with smaller angular wedges, can qualitatively change the evolution of a model. In case of an 11.2 M-circle dot star, the lowest-mass progenitor we investigate, a probably rather weak explosion by the convectively supported neutrino-heating mechanism develops after about 150 ms post-bounce evolution in a 2D simulation with 180 degrees, whereas the same model with 90 degree wedge fails to explode like all other models. This sensitivity demonstrates the proximity of our 2D calculations to the borderline between success and failure, and stresses the need to strive for simulations in 3D, ultimately without the constraints connected with the axis singularity of a polar coordinate grid.