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Title: A Detailed Comparison of Multidimensional Boltzmann Neutrino Transport Methods in Core-collapse Supernovae

Abstract

The mechanism driving core-collapse supernovae is sensitive to the interplay between matter and neutrino radiation. However, neutrino radiation transport is very difficult to simulate, and several radiation transport methods of varying levels of approximation are available. In this paper, we carefully compare for the first time in multiple spatial dimensions the discrete ordinates (DO) code of Nagakura, Yamada, and Sumiyoshi and the Monte Carlo (MC) code Sedonu, under the assumptions of a static fluid background, flat spacetime, elastic scattering, and full special relativity. We find remarkably good agreement in all spectral, angular, and fluid interaction quantities, lending confidence to both methods. The DO method excels in determining the heating and cooling rates in the optically thick region. The MC method predicts sharper angular features due to the effectively infinite angular resolution, but struggles to drive down noise in quantities where subtractive cancellation is prevalent, such as the net gain in the protoneutron star and off-diagonal components of the Eddington tensor. We also find that errors in the angular moments of the distribution functions induced by neglecting velocity dependence are subdominant to those from limited momentum-space resolution. We briefly compare directly computed second angular moments to those predicted by popular algebraicmore » two-moment closures, and we find that the errors from the approximate closures are comparable to the difference between the DO and MC methods. Finally, included in this work is an improved Sedonu code, which now implements a fully special relativistic, time-independent version of the grid-agnostic MC random walk approximation.« less

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [2];  [3]; ORCiD logo [4]; ORCiD logo [5]
  1. California Inst. of Technology (CalTech), Pasadena, CA (United States). Theoretical AstroPhysics Including Relativity and Cosmology (TAPIR). Walter Burke Inst. for Theoretical Physics
  2. California Inst. of Technology (CalTech), Pasadena, CA (United States). Theoretical AstroPhysics Including Relativity and Cosmology (TAPIR). Walter Burke Inst. for Theoretical Physics; Kyoto Univ. (Japan). Center for Gravitational Physics and International Research Unit of Advanced Future Studies. Yukawa Inst. for Theoretical Physics
  3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  4. Numazu College of Technology (Japan)
  5. Waseda Univ., Tokyo (Japan). Advanced Research Inst. for Science & Engineering. Dept. of Science and Engineering
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States); California Inst. of Technology (CalTech), Pasadena, CA (United States); Waseda Univ., Tokyo (Japan); Kyoto Univ. (Japan)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA); LANL Laboratory Directed Research and Development (LDRD) Program; National Science Foundation (NSF); State of Illinois (United States); Japan Society for the Promotion of Science (JSPS); Ministry of Education, Culture, Sports, Science, and Technology (MEXT) (Japan)
OSTI Identifier:
1415403
Report Number(s):
LA-UR-17-24929
Journal ID: ISSN 1538-4357
Grant/Contract Number:
AC52-06NA25396; OCI-0725070; ACI-1238993; TG-PHY100033; ACI-1440083; TCAN AST-1333520; CAREER PHY-1151197; PHY-1404569; 27-348; 15K05093; 16H03986; 26104006
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 847; Journal Issue: 2; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; neutrinos; radiative transfer; supernovae

Citation Formats

Richers, Sherwood, Nagakura, Hiroki, Ott, Christian D., Dolence, Joshua, Sumiyoshi, Kohsuke, and Yamada, Shoichi. A Detailed Comparison of Multidimensional Boltzmann Neutrino Transport Methods in Core-collapse Supernovae. United States: N. p., 2017. Web. doi:10.3847/1538-4357/aa8bb2.
Richers, Sherwood, Nagakura, Hiroki, Ott, Christian D., Dolence, Joshua, Sumiyoshi, Kohsuke, & Yamada, Shoichi. A Detailed Comparison of Multidimensional Boltzmann Neutrino Transport Methods in Core-collapse Supernovae. United States. doi:10.3847/1538-4357/aa8bb2.
Richers, Sherwood, Nagakura, Hiroki, Ott, Christian D., Dolence, Joshua, Sumiyoshi, Kohsuke, and Yamada, Shoichi. 2017. "A Detailed Comparison of Multidimensional Boltzmann Neutrino Transport Methods in Core-collapse Supernovae". United States. doi:10.3847/1538-4357/aa8bb2.
@article{osti_1415403,
title = {A Detailed Comparison of Multidimensional Boltzmann Neutrino Transport Methods in Core-collapse Supernovae},
author = {Richers, Sherwood and Nagakura, Hiroki and Ott, Christian D. and Dolence, Joshua and Sumiyoshi, Kohsuke and Yamada, Shoichi},
abstractNote = {The mechanism driving core-collapse supernovae is sensitive to the interplay between matter and neutrino radiation. However, neutrino radiation transport is very difficult to simulate, and several radiation transport methods of varying levels of approximation are available. In this paper, we carefully compare for the first time in multiple spatial dimensions the discrete ordinates (DO) code of Nagakura, Yamada, and Sumiyoshi and the Monte Carlo (MC) code Sedonu, under the assumptions of a static fluid background, flat spacetime, elastic scattering, and full special relativity. We find remarkably good agreement in all spectral, angular, and fluid interaction quantities, lending confidence to both methods. The DO method excels in determining the heating and cooling rates in the optically thick region. The MC method predicts sharper angular features due to the effectively infinite angular resolution, but struggles to drive down noise in quantities where subtractive cancellation is prevalent, such as the net gain in the protoneutron star and off-diagonal components of the Eddington tensor. We also find that errors in the angular moments of the distribution functions induced by neglecting velocity dependence are subdominant to those from limited momentum-space resolution. We briefly compare directly computed second angular moments to those predicted by popular algebraic two-moment closures, and we find that the errors from the approximate closures are comparable to the difference between the DO and MC methods. Finally, included in this work is an improved Sedonu code, which now implements a fully special relativistic, time-independent version of the grid-agnostic MC random walk approximation.},
doi = {10.3847/1538-4357/aa8bb2},
journal = {The Astrophysical Journal (Online)},
number = 2,
volume = 847,
place = {United States},
year = 2017,
month =
}

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  • We compare Newtonian three-flavor multigroup Boltzmann (MGBT) and (Bruenn`s) multigroup flux-limited diffusion (MGFLD) neutrino transport in postbounce core-collapse supernova environments. We focus our study on quantities central to the postbounce neutrino heating mechanism for reviving the stalled shock. Stationary-state three-flavor neutrino distributions are developed in thermally and hydrodynamically frozen time slices obtained from core collapse and bounce simulations that implement Lagrangian hydrodynamics and MGFLD neutrino transport. We obtain distributions for time slices at 106 and 233 ms after core bounce for the core of a 15 {ital M}{sub {circle_dot}} progenitor, and at 156 ms after core bounce for a 25more » {ital M}{sub {circle_dot}} progenitor. For both transport methods, the electron neutrino and antineutrino luminosities, rms energies, and mean inverse flux factors, all of which enter the neutrino heating rates, are computed as functions of radius and compared. The net neutrino heating rates are also computed as functions of radius and compared. Notably, we find significant differences in neutrino luminosities and mean inverse flux factors between the two transport methods for both precollapse models and for all three time slices. In each case, the luminosities for each transport method begin to diverge above the neutrinospheres, where the MGBT luminosities become larger than their MGFLD counterparts, finally settling to a constant difference maintained to the edge of the core. We find that the mean inverse flux factors, which describe the degree of forward peaking in the neutrino radiation field, also differ significantly between the two transport methods, with MGBT providing more isotropic radiation fields in the gain region. Most important, for a region above the gain radius we find net heating rates for MGBT that are as much as {approximately}2 times the corresponding MGFLD rates, and we find net cooling rates below the gain radius that are typically {approximately}0.8 times the MGFLD rates. These differences stem from differences in the neutrino luminosities and mean inverse flux factors, which can be as much as 11{percent} and 24{percent}, respectively. They are greatest at earlier postbounce times for a given progenitor mass and, for a given postbounce time, greater for greater progenitor mass. We discuss the ramifications that these new results have for the supernova mechanism. {copyright} {ital {copyright} 1998.} {ital The American Astronomical Society}« less
  • With exact three-flavor Boltzmann neutrino transport, we simulate the stellar core collapse, bounce, and postbounce evolution of a 13M{sub 0} star in spherical symmetry, the Newtonian limit, without invoking convection. In the absence of convection, prior spherically symmetric models, which implemented approximations to Boltzmann transport, failed to produce explosions. We consider exact transport to determine if these failures were due to the transport approximations made and to answer remaining fundamental questions in supernova theory. The model presented here is the first in a sequence of models beginning with different progenitors. In this model, a supernova explosion is not obtained.
  • We present numerical results on two- (2D) and three-dimensional (3D) hydrodynamic core-collapse simulations of an 11.2 M {sub ☉} star. By changing numerical resolutions and seed perturbations systematically, we study how the postbounce dynamics are different in 2D and 3D. The calculations were performed with an energy-dependent treatment of the neutrino transport based on the isotropic diffusion source approximation scheme, which we have updated to achieve a very high computational efficiency. All of the computed models in this work, including nine 3D models and fifteen 2D models, exhibit the revival of the stalled bounce shock, leading to the possibility ofmore » explosion. All of them are driven by the neutrino-heating mechanism, which is fostered by neutrino-driven convection and the standing-accretion-shock instability. Reflecting the stochastic nature of multi-dimensional (multi-D) neutrino-driven explosions, the blast morphology changes from model to model. However, we find that the final fate of the multi-D models, whether an explosion is obtained or not, is little affected by the explosion stochasticity. In agreement with some previous studies, higher numerical resolutions lead to slower onset of the shock revival in both 2D and 3D. Based on the self-consistent supernova models leading to the possibility of explosions, our results systematically show that the revived shock expands more energetically in 2D than in 3D.« less
  • We couple two-dimensional hydrodynamics to realistic one-dimensional multigroup flux-limited diffusion neutrino transport to investigate proto{endash}neutron star convection in core-collapse supernovae, and more specifically, the interplay between its development and neutrino transport. Our initial conditions, time-dependent boundary conditions, and neutrino distributions for computing neutrino heating, cooling, and deleptonization rates are obtained from one-dimensional simulations that implement multigroup flux-limited diffusion and one-dimensional hydrodynamics. The development and evolution of proto{endash}neutron star convection are investigated for both 15 and 25M{sub {circle_dot}} models, representative of the two classes of stars with compact and extended iron cores, respectively. For both models, in the absence of neutrinomore » transport, the angle-averaged radial and angular convection velocities in the initial Ledoux unstable region below the shock after bounce achieve their peak values in {approximately}20ms, after which they decrease as the convection in this region dissipates. The dissipation occurs as the gradients are smoothed out by convection. This initial proto{endash}neutron star convection episode seeds additional convectively unstable regions farther out beneath the shock. The additional proto{endash}neutron star convection is driven by successive negative entropy gradients that develop as the shock, in propagating out after core bounce, is successively strengthened and weakened by the oscillating inner core. The convection beneath the shock distorts its sphericity, but on the average the shock radius is not boosted significantly relative to its radius in our corresponding one-dimensional models. In the presence of neutrino transport, proto{endash}neutron star convection velocities are too small relative to bulk inflow velocities to result in any significant convective transport of entropy and leptons. This is evident in our two-dimensional entropy snapshots, which in this case appear spherically symmetric. The peak angle-averaged radial and angular convection velocities are orders of magnitude smaller than they are in the corresponding {open_quotes}hydrodynamics-only{close_quotes} models. A simple analytical model supports our numerical results, indicating that the inclusion of neutrino transport reduces the entropy-driven (lepton-driven) convection growth rates and asymptotic velocities by a factor {approximately}3 (50) at the neutrinosphere and a factor {approximately}250 (1000) at {rho}=10{sup 12}gcm{sup {minus}3}, for both our 15 and 25M{sub {circle_dot}} models. Moreover, when transport is included, the initial postbounce entropy gradient is smoothed out by neutrino diffusion, whereas the initial lepton gradient is maintained by electron capture and neutrino escape near the neutrinosphere. Despite the maintenance of the lepton gradient, proto{endash}neutron star convection does not develop over the 100 ms duration typical of all our simulations, except in the instance where {open_quotes}low-test{close_quotes} initial conditions are used, which are generated by core-collapse and bounce simulations that neglect neutrino{endash}electron scattering and ion{endash}ion screening corrections to neutrino{endash}nucleus elastic scattering. Models favoring the development of proto{endash}neutron star convection either by starting with more favorable, albeit artificial (low-test), initial conditions or by including transport corrections that were ignored in our {open_quotes}fiducial{close_quotes} models were considered. Our conclusions nonetheless remained the same. Evidence of proto{endash}neutron star convection in our two-dimensional entropy snapshots was minimal, and, as in our fiducial models, the angle-averaged convective velocities when neutrino transport was included remained orders of magnitude smaller than their counterparts in the corresponding hydrodynamics-only models. {copyright} {ital 1998} {ital The American Astronomical Society}« less