4 research outputs found
High-resolution supernova neutrino spectra represented by a simple fit
To study the capabilities of supernova neutrino detectors, the instantaneous
spectra are often represented by a quasi-thermal distribution of the form f(E)
= E^alpha e^{-(alpha+1)E/E_{av}} where E_{av} is the average energy and alpha a
numerical parameter. Based on a spherically symmetric supernova model with full
Boltzmann neutrino transport we have, at a few representative post-bounce
times, re-converged the models with vastly increased energy resolution to test
the fit quality. For our examples, the spectra are well represented by such a
fit in the sense that the counting rates for a broad range of target nuclei,
sensitive to different parts of the spectrum, are reproduced very well.
Therefore, the mean energy and root-mean-square energy of numerical spectra
hold enough information to provide the correct alpha and to forecast the
response of multi-channel supernova neutrino detection.Comment: 6 pages, including 4 figures and 2 tables. Clarifying paragraphs
added; results unchanged. Matches published version in PR
Impact of neutrino flavor oscillations on the neutrino-driven wind nucleosynthesis of an electron-capture supernova
Neutrino oscillations, especially to light sterile states, can affect the
nucleosynthesis yields because of their possible feedback effect on the
electron fraction (Ye). For the first time, we perform nucleosynthesis
calculations for neutrino-driven wind trajectories from the neutrino-cooling
phase of an 8.8 Msun electron-capture supernova, whose hydrodynamic evolution
was computed in spherical symmetry with sophisticated neutrino transport and
whose Ye evolution was post-processed by including neutrino oscillations both
between active and active-sterile flavors. We also take into account the
alpha-effect as well as weak magnetism and recoil corrections in the neutrino
absorption and emission processes. We observe effects on the Ye evolution which
depend in a subtle way on the relative radial positions of the sterile MSW
resonances, of collective flavor transformations, and on the formation of alpha
particles. For the adopted supernova progenitor, we find that neutrino
oscillations, also to a sterile state with eV-mass, do not significantly affect
the element formation and in particular cannot make the post-explosion wind
outflow neutron rich enough to activate a strong r-process. Our conclusions
become even more robust when, in order to mimic equation-of-state dependent
corrections due to nucleon potential effects in the dense-medium neutrino
opacities, six cases with reduced Ye in the wind are considered. In these
cases, despite the conversion of active neutrinos to sterile neutrinos, Ye
increases or is not significantly lowered compared to the values obtained
without oscillations and active flavor transformations. This is a consequence
of a complicated interplay between sterile-neutrino production,
neutrino-neutrino interactions, and alpha-effect.Comment: 19 pages, 12 figures; accepted for publication by Ap
Core-Collapse Supernovae: Reflections and Directions
Core-collapse supernovae are among the most fascinating phenomena in
astrophysics and provide a formidable challenge for theoretical investigation.
They mark the spectacular end of the lives of massive stars and, in an
explosive eruption, release as much energy as the sun produces during its whole
life. A better understanding of the astrophysical role of supernovae as birth
sites of neutron stars, black holes, and heavy chemical elements, and more
reliable predictions of the observable signals from stellar death events are
tightly linked to the solution of the long-standing puzzle how collapsing stars
achieve to explode. In this article our current knowledge of the processes that
contribute to the success of the explosion mechanism are concisely reviewed.
After a short overview of the sequence of stages of stellar core-collapse
events, the general properties of the progenitor-dependent neutrino emission
will be briefly described. Applying sophisticated neutrino transport in
axisymmetric (2D) simulations with general relativity as well as in simulations
with an approximate treatment of relativistic effects, we could find successful
neutrino-driven explosions for a growing set of progenitor stars. First results
of three-dimensional (3D) models have been obtained, and magnetohydrodynamic
simulations demonstrate that strong initial magnetic fields in the pre-collapse
core can foster the onset of neutrino-powered supernova explosions even in
nonrotating stars. These results are discussed in the context of the present
controversy about the value of 2D simulations for exploring the supernova
mechanism in realistic 3D environments, and they are interpreted against the
background of the current disagreement on the question whether the standing
accretion shock instability (SASI) or neutrino-driven convection is the crucial
agency that supports the onset of the explosion.Comment: 36 pages, 20 figures (43 eps files); submitted to Progress of
Theoretical and Experimental Physics (PTEP
Flavor-dependent neutrino angular distribution in core-collapse supernovae
According to recent studies, the collective flavor evolution of neutrinos in
core-collapse supernovae depends strongly on the flavor-dependent angular
distribution of the local neutrino radiation field, notably on the angular
intensity of the electron-lepton number carried by neutrinos. To facilitate
further investigations of this subject, we study the energy and angle
distributions of the neutrino radiation field computed with the Vertex
neutrino-transport code for several spherically symmetric (1D) supernova
simulations (of progenitor masses 11.2, 15 and 25 M_sun) and explain how to
extract this information from additional models of the Garching group.
Beginning in the decoupling region ("neutrino sphere"), the distributions are
more and more forward peaked in the radial direction with an angular spread
that is largest for , smaller for , and smallest for ,
where or . While the energy-integrated minus
angle distribution has a dip in the forward direction, it does not turn
negative in any of our investigated cases.Comment: 10 pages, including 8 figures. Minor changes in the text, matches
version accepted for publication in ApJ. Data and animated visualization
available at:
http://wwwmpa.mpa-garching.mpg.de/ccsnarchive/data/Tamborra2017