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Register a new userThree-dimensional neutrino-driven supernovae: Neutron star kicks, spins, and asymmetric ejection of nucleosynthesis products
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Annop Wongwathanarat
Publication date
2012
fields
Physics
and research's language is
English
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We present 3D simulations of supernova (SN) explosions of nonrotating stars, triggered by the neutrino-heating mechanism with a suitable choice of the core-neutrino luminosity. Our results show that asymmetric mass ejection caused by hydrodynamic instabilities can accelerate the neutron star (NS) up to recoil velocities of more than 700 km/s by the gravitational tug-boat mechanism, which is enough to explain most observed pulsar velocities. The associated NS spin periods are about 100 ms to 8 s without any correlation between spin and kick magnitudes or directions. This suggests that faster spins and a possible spin-kick alignment might require angular momentum in the progenitor core prior to collapse. Our simulations for the first time demonstrate a clear correlation between the size of the NS kick and anisotropic ejection of heavy elements created by explosive burning behind the shock. In the case of large NS kicks the explosion is significantly stronger opposite to the kick vector. Therefore the bulk of the Fe-group elements, in particular nickel, is ejected mostly in large clumps against the kick direction. This contrasts with the case of low recoil velocity, where the Ni-rich lumps are more isotropically distributed. Intermediate-mass nuclei heavier than Si (like Ca and Ti) also exhibit a significant enhancement in the hemisphere opposite to the direction of fast NS motion, while the distribution of C, O, and Ne is not affected, and that of Mg only marginally. Mapping the spatial distribution of the heavy elements in SN remnants with identified pulsar motion may offer an important diagnostic test of the kick mechanism. Different from kick scenarios based on anisotropic neutrino emission, our hydrodynamical acceleration model predicts enhanced ejection of Fe-group elements and of their nuclear precursors in the direction opposite to the NS recoil. (abridged)
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We propose a simple model to explain the velocity of young neutron stars. We attempt to confirm a relationship between the amount of mass ejected in the formation of the neutron star and the `kick velocity imparted to the compact remnant resulting from the process. We assume the velocity is given by $v_{rm kick}=alpha,(M_{rm ejecta} / M_{rm remnant}) + beta,$. To test this simple relationship we use the BPASS (Binary Population and Spectral Synthesis) code to create stellar population models from both single and binary star evolutionary pathways. We then use our Remnant Ejecta and Progenitor Explosion Relationship (REAPER) code to apply different $alpha$ and $beta$ values and three different `kick orientations then record the resulting velocity probability distributions. We find that while a single star population provides a poor fit to the observational data, the binary population provides an excellent fit. Values of $alpha=70, {rm km,s^{-1}}$ and $beta=110,{rm km,s^{-1}}$ reproduce the cite{RN165} observed 2-dimensional velocities and $alpha=70, {rm km,s^{-1}}$ and $beta=120,{rm km,s^{-1}}$ reproduce their inferred 3-dimensional velocity distribution for nearby single neutron stars with ages less than 3 Myrs. After testing isotropic, spin-axis aligned and orthogonal to spin-axis `kick orientations, we find no statistical preference for a `kick orientation. While ejecta mass cannot be the only factor that determines the velocity of supernovae compact remnants, we suggest it is a significant contributor and that the ejecta based `kick should replace the Maxwell-Boltzmann velocity distribution currently used in many population synthesis codes.
Observations of radio pulsars have revealed that they have large velocities which may be greater than 1000 km/s. In this work, the efficacy of an active-sterile neutrino transformation mechanism to provide these large pulsar kicks is investigated. A phase-space based approach is adopted to follow the the transformation of active neutrinos to sterile neutrinos through an MSW-like resonance in the protoneutron star to refine an estimate to the magnitude of the pulsar kick that can be generated in such an event. The result is that this mechanism can create the large pulsar kicks that are observed while not overcooling the star.
Neutrinos from a supernova (SN) might undergo fast flavor
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