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Register a new userNeutrino signatures of near-critical supernova outflows
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Added by
Alexander Friedland
Publication date
2020
fields
Physics
and research's language is
English
Authors
Alexander Friedland
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In a core-collapse supernova, after the explosion is launched, neutrino heating above the protoneutron star creates an outflow of matter. This outflow has been extensively investigated as a nucleosynthesis site. Here, we revisit this problem motivated by the modeling of neutrino flavor transformations. In this case, it is crucial to understand whether the outflow has a termination shock: its existence observably alters neutrino oscillations a few seconds into the explosion. We derive physical criteria for the formation of this shock, in terms of neutrino luminosity, average energy, protoneutron star radius and mass, and the postshock density. For realistic physical conditions, the system is found to be on the edge of shock formation, thus reconciling seemingly disparate numerical results in the literature. Our findings imply that neutrino signatures of modulated matter effects are a sensitive probe of the inner workings of the supernova.
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A suite of detectors around the world is poised to measure the flavor-energy-time evolution of the ten-second burst of neutrinos from a core-collapse supernova occurring in the Milky Way or nearby. Next-generation detectors to be built in the next decade will have enhanced flavor sensitivity and statistics. Not only will the observation of this burst allow us to peer inside the dense matter of the extreme event and learn about the collapse processes and the birth of the remnant, but the neutrinos will bring information about neutrino properties themselves. This review surveys some of the physical signatures that the currently-unknown neutrino mass pattern will imprint on the observed neutrino events at Earth, emphasizing the most robust and least model-dependent signatures of mass ordering.
We present the first self-consistent, three-dimensional (3D) core-collapse supernova simulations performed with the Prometheus-Vertex code for a rotating progenitor star. Besides using the angular momentum of the 15 solar-mass model as obtained in the stellar evolution calculation with an angular frequency of about 0.001 rad/s (spin period of more than 6000 s) at the Si/Si-O interface, we also computed 2D and 3D cases with no rotation and with a ~300 times shorter rotation period and different angular resolutions. In 2D, only the nonrotating and slowly rotating models explode, while rapid rotation prevents an explosion within 500 ms after bounce because of lower radiated neutrino luminosities and mean energies and thus reduced neutrino heating. In contrast, only the fast rotating model develops an explosion in 3D when the Si/Si-O interface collapses through the shock. The explosion becomes possible by the support of a powerful SASI spiral mode, which compensates for the reduced neutrino heating and pushes strong shock expansion in the equatorial plane. Fast rotation in 3D leads to a two-dimensionalization of the turbulent energy spectrum (yielding roughly a -3 instead of a -5/3 power-law slope at intermediate wavelengths) with enhanced kinetic energy on the largest spatial scales. We also introduce a generalization of the universal critical luminosity condition of Summa et al. (2016) to account for the effects of rotation, and demonstrate its viability for a set of more than 40 core-collapse simulations including 9 and 20 solar-mass progenitors as well as black-hole forming cases of 40 and 75 solar-mass stars to be discussed in forthcoming papers.
The late-time evolution of the neutrino event rate from supernovae is evaluated for Super-Kamiokande using simulated results of proto-neutron star (PNS) cooling. In the present work we extend the result of Suwa et al. (2019) [arXiv:1904.09996], which studied the dependence on the PNS mass, but focus on the impact of the nuclear equation of state (EOS). We find that the neutrino event rate depends on both the high-density and low-density EOS, where the former determines the radius of the PNS and the latter affects its surface temperature. Based on the present evaluation of the neutrino event rate we propose a new analysis method to extract the time variability of the neutrino average energy taking into account the statistical error in the observation.
Supernova neutrinos are crucially important to probe the final phases of massive star evolution. As is well known from observations of SN1987A, neutrinos provide information on the physical conditions responsible for neutron star formation and on the supernova explosion mechanism. However, there is still no complete understanding of the long-term evolution of neutrino emission in supernova explosions, although there are a number of modern simulations of neutrino radiation hydrodynamics, which study neutrino emission at times less than one second after the bounce. In the present work we systematically calculate the number of neutrinos that can be observed in Super-Kamiokande over periods longer than ten seconds using the database of Nakazato et al. (2013) anticipating that neutrinos from a Galactic supernova can be detected for several tens of seconds. We find that for a supernova at a distance of 10 kpc, neutrinos remain observable for longer than 30 s for a low-mass neutron star ($1.20M_odot$ gravitational mass) and even longer than 100 s for a high-mass neutron star ($2.05M_odot$). These scenarios are much longer than the observations of SN1987A and longer than the duration of existing numerical simulations. We propose a new analysis method based on the cumulative neutrino event distribution as a function of reverse time from the last observed event, as a useful probe of the neutron star mass. Our result demonstrates the importance of complete modeling of neutrino light curves in order to extract physical quantities essential for understanding supernova explosion mechanisms, such as the mass and radius of the resulting neutron star.
We reinvestigate effects of neutrino oscillations on the production of 7Li and 11B in core-collapse supernovae (SNe). During the propagation of neutrinos from the proto-neutron star, their flavors change and the neutrino reaction rates for spallation of 12C and 4He are affected. In this work corrected neutrino spallation cross sections for 4He and 12C are adopted. Initial abundances involving heavy s-nuclei and other physical conditions are derived in a new calculation of the SN 1987A progenitor in which effects of the progenitor metallicity are included. A dependence of the SN nucleosynthesis and final yields of 7Li and 11B on the neutrino mass hierarchy are shown in several stellar locations. In the normal hierarchy case, the charged current reaction rates of electron neutrinos are enhanced, and yields of proton-rich nuclei, along with 7Be and 11C, are increased. In the inverted hierarchy case, the charged current reaction rates of electron antineutrinos are enhanced, and yields of neutron-rich nuclei, along with 7Li and 11B, are increased. We find that variation of the metallicity modifies the yields of 7Li, 7Be, 11B, and 11C. This effect is caused by changes in the neutron abundance during SN nucleosynthesis. Therefore, accurate calculations of Li and B production in SNe should take into account the metallicity of progenitor stars.
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