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An 8.8 M⊙ electron-capture supernova was simulated in spherical symmetry consistently from collapse through explosion to essentially complete deleptonization of the forming neutron star. The evolution time (∼ 9 s) is short because high-density effects suppress our neutrino opacities. After a short phase of accretion-enhanced luminosities (∼200 ms), luminosity equipartition among all species becomes almost perfect and the spectra ofνe andνµ,τ very similar, ruling out the neutrino-driven wind as r-process site. We also discuss consequences for neutrino flavor oscillations.PACS numbers: 97.60. Bw, 95.85.Ry, 97.60.Jd Introduction.-During the first seconds after collapse, a supernova (SN) core emits its binding energy, roughly 10% of its rest mass, in the form of neutrinos. In the delayed explosion paradigm, supported at least for some progenitor stars by recent simulations [1], neutrinos revive the stalled shock wave and by their energy deposition explode the star [2]. Later they drive a powerful wind and through β-processes determine its role as a possible site for r-process nucleosynthesis [3]. Inevitable deviations from spherical symmetry allow the neutrino flux to emit gravitational waves [4] and to impart a potentially large neutron-star recoil [5].A sparse neutrino signal was observed from SN 1987A. Existing and foreseen large detectors [6] will operate for decades, suggesting the next galactic SN will provide a high-statistics signal and allow for a direct glance of its inner workings. The cosmic diffuse neutrino background from all past SNe (DSNB) is almost certainly detectable if gadolinium loading of Super-Kamiokande succeeds [7] or by future large scintillator detectors [8], pushing the frontiers of neutrino astronomy to cosmic distances.The fluxes and spectra differ for the species ν e ,ν e and ν x (representing any of ν µ,τ orν µ,τ ). Flavor oscillations swap ν e ↔ ν x andν e ↔ν x in part or completely, a process strongly affected by collective effects and MikheevSmirnov-Wolfenstein resonances [9]. What is seen in the neutrino-driven wind or by a detector thus depends not only on what is emitted, but also on the matter profile and neutrino mixing parameters.Quantitative studies in these areas are impeded by large uncertainties of the expected fluxes and spectra. This problem partly derives from uncertainties of the explosion mechanism itself and input physics such as the nuclear equation of state (EoS). Significant variations are expected in dependence of the progenitor mass, and sometimes rotation and magnetic fields may come into play. However, even without such complications, the range of predictions is large for the post-explosion cooling phase when by far most of the neutrino loss happens.The pioneering work of the Livermore group combined relativistic hydrodynamics with multi-group three-flavor

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.Subject Index: 483, 421, 423, 415, 451, 452, 242 §1. Supernova theory in a nutshell Massive stars in the range between ∼8 M ⊙ and several 10 M ⊙ develop lowentropy cores, in which relativistic electrons dominate the pressure. Heavy nuclei yield only a small, though important, contribution to providing stabilization against the inward pull of gravity. The core consists of the final products of the star's nuclear burning history. It is surrounded by concentric shells that, from outside inward, contain the successively heavier ashes of all previous burning stages (Fig. 1).Shell burning leads to a continuous growth of the mass of the central core until gravitational instability finally sets in. At this time the core resembles a hot white dwarf close to its maximum mass of the order of the Chandrasekhar mass. It has typeset using PTPT E X.cls Ver.0.9 * ) The effective (dynamically relevant) adiabatic index is defined as the logarithmic density derivative of the pressure, (∂ ln P/∂ ln ρ) m , along a fluid element's trajectory, averaged over the volume of the collapsing core. It governs the transition to gravitational instability and the collapse dynamics. 1) ...

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

17 pages, 5 figuresInternational audienceThe rise time of a Galactic supernova (SN) bar-nue lightcurve, observable at a high-statistics experiment such as the IceCube Cherenkov detector, can provide a diagnostic tool for the neutrino mass hierarchy at "large" 1-3 leptonic mixing angle theta_13. Thanks to the combination of matter suppression of collective effects at early postbounce times on one hand and the presence of the ordinary Mikheyev-Smirnov-Wolfenstein effect in the outer layers of the SN on the other hand, a sufficiently fast rise time on O(100) ms scale is indicative of an inverted mass hierarchy. We investigate results from an extensive set of stellar core-collapse simulations, providing a first exploration of the astrophysical robustness of these features. We find that for all the models analyzed (sharing the same weak interaction microphysics) the rise times for the same hierarchy are similar not only qualitatively, but also quantitatively, with the signals for the two classes of hierarchies significantly separated. We show via Monte Carlo simulations that the two cases should be distinguishable at IceCube for SNe at a typical Galactic distance 99% of the times. Finally, a preliminary survey seems to show that the faster rise time for inverted hierarchy as compared to normal hierarchy is a qualitatively robust feature predicted by several simulation groups. Since the viability of this signature ultimately depends on the quantitative assessment of theoretical/numerical uncertainties, our results motivate an extensive campaign of comparison of different code predictions at early accretion times with implementation of microphysics of comparable sophistication, including effects such like nucleon recoils in weak interactions

Self-induced flavor conversions of supernova (SN) neutrinos can strongly modify the flavor dependent fluxes. We perform a linearized flavor stability analysis with accretion-phase matter profiles of a 15 M spherically symmetric model and corresponding neutrino fluxes. We use realistic energy and angle distributions, the latter deviating strongly from quasi-isotropic emission, thus accounting for both multi-angle and multi-energy effects. For our matter and neutrino density profile we always find stable conditions: flavor conversions are limited to the usual Mikheyev-Smirnov-Wolfenstein effect. In this case one may distinguish the neutrino mass hierarchy in a SN neutrino signal if the mixing angle θ13 is as large as suggested by recent experiments.PACS numbers: 97.60.Bw, 14.60.PqIntroduction.-The huge neutrino fluxes emitted by core-collapse supernovae (SNe) are key to the explosion dynamics and nucleosynthesis [1] and detecting a highstatistics "neutrino light curve" from the next nearby SN is a major goal for neutrino astronomy [2]. Besides probing the core-collapse phenomenon in unprecedented detail, one may detect signatures of flavor oscillations and extract information on neutrino mixing parameters [3,4].The refractive effect caused by matter [5] suppresses flavor oscillations until neutrinos pass through the Mikheyev-Smirnov-Wolfenstein (MSW) region in the collapsing star's envelope [6,7]. However, neutrino-neutrino interactions, through a flavor off-diagonal refractive index [8,9], can trigger self-induced flavor conversions [10][11][12]. This collective effect usually occurs between the neutrino sphere and the MSW region and can strongly modify neutrino spectra [13][14][15], although this would never seem to help explode the star [16]. Actually, in lowmass SNe (not studied here) the density falls off so fast that MSW can occur first, leading to novel effects on the prompt ν e burst [17].Collective oscillations at first seemed unaffected by matter because its influence does not depend on neutrino energies [13]. However, depending on emission angle, neutrinos accrue different matter-induced flavordependent phases until they reach a given radius. This "multi-angle matter effect" can suppress self-induced flavor conversion [18]. Based on schematic flux spectra, this was numerically confirmed for accretion-phase SN models where the density near the core is large [19]. This epoch, before the delayed explosion finally takes off, is when the neutrino luminosity and the difference between theν e andν µ,τ fluxes are largest. If self-induced flavor conversion did not occur and the mixing angle θ 13 was not very small [20], the accretion phase would provide a plausible opportunity to determine the mass hierarchy [3,19].Numerical multi-angle simulations of collective oscillations are very demanding [21], but it is much easier to

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 neutrinotransport code for several spherically symmetric (1D) supernova simulations (of progenitor masses 11.2, 15 and 25 M ) 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 ν e , smaller forν e , and smallest for ν x , where x = µ or τ. While the energy-integrated ν e minusν e angle distribution has a dip in the forward direction, it does not turn negative in any of our investigated cases.

Abstract. Motivated by recent hints for sterile neutrinos from the reactor anomaly, we study active-sterile conversions in a three-flavor scenario (2 active + 1 sterile families) for three different representative times during the neutrino-cooling evolution of the proto-neutron star born in an electron-capture supernova. In our "early model" (0.5 s post bounce), the ν e -ν s MSW effect driven by ∆m 2 = 2.35 eV 2 is dominated by ordinary matter and leads to a complete ν e -ν s swap with little or no trace of collective flavor oscillations. In our "intermediate" (2.9 s p.b.) and "late models" (6.5 s p.b.), neutrinos themselves significantly modify the ν e -ν s matter effect, and, in particular in the late model, νν refraction strongly reduces the matter effect, largely suppressing the overall ν e -ν s MSW conversion. This phenomenon has not been reported in previous studies of active-sterile supernova neutrino oscillations. We always include the feedback effect on the electron fraction Y e due to neutrino oscillations. In all examples, Y e is reduced and therefore the presence of sterile neutrinos can affect the conditions for heavy-element formation in the supernova ejecta, even if probably not enabling the r-process in the investigated outflows of an electron-capture supernova. The impact of neutrino-neutrino refraction is strong but complicated, leaving open the possibility that with a more complete treatment, or for other supernova models, active-sterile neutrino oscillations could generate conditions suitable for the r-process.