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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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DOE OSTI2013

THE VERTICAL COMPOSITION OF NEUTRINO-DOMINATED ACCRETION DISKS IN GAMMA-RAY BURSTS

We investigate the vertical structure and element distribution of neutrino-dominated accretion flows around black holes in spherical coordinates using the reasonable nuclear statistical equilibrium. According to our calculations, heavy nuclei tend to be produced in a thin region near the disk surface, whose mass fractions are primarily determined by the accretion rate and vertical distribution of temperature and density. In this thin region, we find that {sup 56}Ni is dominant for the flow with a low accretion rate (e.g., 0.05 M {sub Sun} s{sup -1}), but {sup 56}Fe is dominant for the flow with a high accretion rate (e.g., 1 M {sub Sun} s{sup -1}). The dominant {sup 56}Ni in the aforementioned region may provide a clue to understanding the bumps in the optical light curve of core-collapse supernovae.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

Late-time photometry of type IA supernova SN 2012cg reveals the radioactive decay of {sup 57}Co

Seitenzahl et al. have predicted that roughly three years after its explosion, the light we receive from a Type Ia supernova (SN Ia) will come mostly from reprocessing of electrons and X-rays emitted by the radioactive decay chain {sup 57}Co → {sup 57}Fe, instead of positrons from the decay chain {sup 56}Co → {sup 56}Fe that dominates the SN light at earlier times. Using the Hubble Space Telescope, we followed the light curve of the SN Ia SN 2012cg out to 1055 days after maximum light. Our measurements are consistent with the light curves predicted by the contribution of energy from the reprocessing of electrons and X-rays emitted by the decay of {sup 57}Co, offering evidence that {sup 57}Co is produced in SN Ia explosions. However, the data are also consistent with a light echo ∼14 mag fainter than SN 2012cg at peak. Assuming no light-echo contamination, the mass ratio of {sup 57}Ni and {sup 56}Ni produced by the explosion, a strong constraint on any SN Ia explosion models, is 0.043{sub −0.011}{sup +0.012}, roughly twice Solar. In the context of current explosion models, this value favors a progenitor white dwarf with a mass near the Chandrasekhar limit.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2011

Nuclear Data Sheets for A = 56

The 1999 publication of Nuclear Data Sheets for A=56 (1999Hu04) has been updated using experimental nuclear structure data and decay data available before November 2009. The information for {sup 56}K, {sup 56}Ca, {sup 56}Sc, {sup 56}Ti, {sup 56}V, {sup 56}Cr, {sup 56}Mn, {sup 56}Fe, {sup 56}Co, {sup 56}Ni, {sup 56}Cu, and {sup 56}Zn from various reaction and decay experiments together with their adopted levels and {gamma} transition properties is summarized and presented.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2015

A LUMINOUS, FAST RISING UV-TRANSIENT DISCOVERED BY ROTSE: A TIDAL DISRUPTION EVENT?

We present follow-up observations of an optical transient (OT) discovered by ROTSE on 2009 January 21. Photometric monitoring was carried out with ROTSE-IIIb in the optical and Swift in the UV up to +70 days after discovery. The light curve showed a fast rise time of ∼10 days followed by a steep decline over the next 60 days, which was much faster than that implied by {sup 56}Ni—{sup 56}Co radioactive decay. The Sloan Digital Sky Survey Data Release 10 database contains a faint, red object at the position of the OT, which appears slightly extended. This and other lines of evidence suggest that the OT is of extragalactic origin, and this faint object is likely the host galaxy. A sequence of optical spectra obtained with the 9.2 m Hobby-Eberly Telescope between +8 and +45 days after discovery revealed a hot, blue continuum with no visible spectral features. A few weak features that appeared after +30 days probably originated from the underlying host. Fitting synthetic templates to the observed spectrum of the host galaxy revealed a redshift of z = 0.19. At this redshift, the peak magnitude of the OT is close to –22.5, similar to the brightest super-luminous supernovae; however, the lack of identifiable spectral features makes the massive stellar death hypothesis less likely. A more plausible explanation appears to be the tidal disruption of a Sun-like star by the central supermassive black hole. We argue that this transient likely belongs to a class of super-Eddington tidal disruption events.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

A new insight into neutrino energy loss by electron capture of iron group nuclei in magnetar surfaces

Based on the relativistic mean-field effective interactions theory, and the Lai dong model, we discuss the influences of superstrong magnetic fields (SMFs) on electron Fermi energy, nuclear blinding energy, and single-particle level structure in magnetar surfaces. Using the Shell-Model Monte Carlo method and the Random Phase Approximation theory, we analyze the neutrino energy loss rates (NELRs) by electron capture for iron group nuclei in SMFs. First, when B {sub 12} < 100, we find that the SMFs have a slight influence on the NELRs for most nuclides at relativistic low temperatures (e.g., T {sub 9} = 0.233); nevertheless, the NELRs increase by more than four orders of magnitude at relativistic high temperatures (e.g., T {sub 9} = 15.53). When B {sub 12} > 100, the NELRs decrease by more than three orders of magnitude (e.g., at T {sub 9} = 15.53 for {sup 52–61}Fe, {sup 55–60}Co, and {sup 56–63}Ni). Second, for a certain value of magnetic field and temperature, the NELRs increase by more than four orders of magnitude when ρ{sub 7}⩽10{sup 3}, but as the density increases (i.e., when ρ{sub 7}>10{sup 3}), there is almost no influence on the density of NELRs. For the density around ρ{sub 7}=10{sup 2}, there is an abrupt increase in NELRs when B {sub 12} ≥ 10{sup 3.5}. Such jumps are an indication that the underlying shell structure has changed due to single-particle behavior by SMFs. Finally, we compare our NELRs with those of Fuller et al. (FFN) and Nabi and Klapdor-Kleingrothaus (NKK). For the case without SMFs, one finds that our rates for certain nuclei are close to about five orders of magnitude lower than FFN and NKK at relativistic low temperatures (e.g., T {sub 9} = 1). However, at a relativistic high temperature (e.g., T {sub 9} = 3), our results are in good agreement with NKK, but about one order of magnitude lower than FFN. For the case with SMFs, our NELRs for some iron group nuclei can be about five orders of magnitude higher than those of FFN and NKK. (Note that B {sub 12}, T {sub 9}, and ρ {sub 7} are in units of 10{sup 12} G, 10{sup 9} K, and 10{sup 7} g cm{sup −3}, respectively.)

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2011

Spallation Model for the Titanium-Rich Supernova Remnant Cassiopeia A

Titanium-rich subluminous supernovae are rare and challenge current SN nucleosynthesis models. We present a model in which ejecta from a standard supernova is impacted by a second explosion of the neutron star (a quark nova), resulting in spallation reactions that lead to {sup 56}Ni destruction and {sup 44}Ti creation under the right conditions. Basic calculations of the spallation products shows that a delay between the two explosions of {approx}5 days reproduces the observed abundance of {sup 44}Ti in Cas A and explains its low luminosity as a result of the destruction of {sup 56}Ni. Our results could have important implications for light curves of subluminous as well as superluminous supernovae.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2011

THE MOST SLOWLY DECLINING TYPE Ia SUPERNOVA 2001ay

We present optical and near-infrared photometry, as well as ground-based optical spectra and Hubble Space Telescope ultraviolet spectra, of the Type Ia supernova (SN) 2001ay. At maximum light the Si II and Mg II lines indicated expansion velocities of 14,000 km s{sup -1}, while Si III and S II showed velocities of 9000 km s{sup -1}. There is also evidence for some unburned carbon at 12,000 km s{sup -1}. SN 2001ay exhibited a decline-rate parameter of {Delta}m{sub 15}(B) = 0.68 {+-} 0.05 mag; this and the B-band photometry at t {approx}> +25 day past maximum make it the most slowly declining Type Ia SN yet discovered. Three of the four super-Chandrasekhar-mass candidates have decline rates almost as slow as this. After correction for Galactic and host-galaxy extinction, SN 2001ay had M{sub B} = -19.19 and M{sub V} = -19.17 mag at maximum light; thus, it was not overluminous in optical bands. In near-infrared bands it was overluminous only at the 2{sigma} level at most. For a rise time of 18 days (explosion to bolometric maximum) the implied {sup 56}Ni yield was (0.58 {+-} 0.15)/{alpha} M{sub sun}, with {alpha} = L{sub max}/E{sub Ni} probably in the range 1.0-1.2. The {sup 56}Ni yield is comparable to that of many Type Ia SNe. The 'normal' {sup 56}Ni yield and the typical peak optical brightness suggest that the very broad optical light curve is explained by the trapping of {gamma} rays in the inner regions.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2011

Evaluation of electron capture reaction rates in Ni isotopes in stellar environments

Electron capture rates in Ni isotopes are studied in stellar environments, that is, at high densities and high temperatures during the core-collapse and postbounce explosive nucleosynthesis in supernovae. Reaction rates in {sup 58}Ni and {sup 60}Ni, as well as in {sup 56}Ni, {sup 62}Ni, and {sup 64}Ni, are evaluated by shell-model calculations with the use of a new shell-model Hamiltonian in the fp shell, GXPF1J. While the previous shell-model calculations failed to reproduce the measured peaks of Gamow-Teller strength in {sup 58}Ni and {sup 60}Ni, the present new Hamiltonian is found to reproduce them very well, as well as the capture rates obtained from the observed strengths. Strengths and energies of the Gamow-Teller transitions in {sup 56}Ni, {sup 62}Ni, and {sup 64}Ni are also found to be consistent with the observations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2011

PHOTOMETRIC EVOLUTION OF SNe Ib/c 2004ao, 2004gk, AND 2006gi

Photometric observations of three core collapse supernovae (SNe 2004ao, 2004gk, and 2006gi), covering about 200 days of evolution, are presented and analyzed. The photometric behavior of the three objects is consistent with their membership in the envelope-stripped Type Ib/c class. Pseudobolometric light curves are constructed. The corresponding measured e-folding times are found to be faster compared to the {sup 56}Co decay (i.e., 111.3 days), suggesting that a proportion of {gamma}-rays increasing with time have escaped without thermalization, owing to the low-mass nature of the ejecta. SN 2006gi has almost identical post-maximum decline phase luminosities as SN 1999ex and found to be similar to both SNe 1999dn and 1999ex in terms of the quasi-bolometric shape, placing it among the fast decliner Ib objects. SN 2004ao appears to fit within the slow decliner Ib SNe. SNe 2004ao and 2004gk display almost identical luminosities in the [50-100] day time interval, similar to SN 1993J. A preliminary simplified {gamma}-ray deposition model is described and applied to the computed pseudobolometric light curves, allowing one to find a range in the ejecta and {sup 56}Ni masses. The optical and quasi-bolometric light curves and the B - V color evolution of SN 2004gk are found to show a sudden drop after day 150. Correlating this fact to dust formation is premature and requires further observational evidence.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2011

Clusterization in the shape isomers of the {sup 56}Ni nucleus

The interrelation of the quadrupole deformation and clusterization is investigated in the example of the {sup 56}Ni nucleus. The shape isomers, including superdeformed and hyperdeformed states, are obtained as stability regions of the quasidynamical U(3) symmetry based on a Nilsson calculation. Their possible binary clusterizations are investigated by considering both the consequences of the Pauli exclusion principle and the energetic preference.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2011

Extrapolation method in the Monte Carlo Shell Model and its applications

We demonstrate how the energy-variance extrapolation method works using the sequence of the approximated wave functions obtained by the Monte Carlo Shell Model (MCSM), taking {sup 56}Ni with pf-shell as an example. The extrapolation method is shown to work well even in the case that the MCSM shows slow convergence, such as {sup 72}Ge with f5pg9-shell. The structure of {sup 72}Se is also studied including the discussion of the shape-coexistence phenomenon.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2011

Neutrino-Nucleus Reactions at MeV Region based on New Shell-Model Hamiltonians

Neutrino-nucleus reactions at MeV region are evaluated by using new shell model Hamiltonians, which are found to improve the description of spin degrees of freedom in nuclei as well as shell evolutions. The light element synthesis by neutrino processes in supernova explosions is discussed with the use of the new reaction cross sections for {sup 12}C and {sup 4}He. Possible constraints on the mixing angle {theta}{sub 13} and the neutrino mass hierarchy are pointed out to be imposed by the production yields of {sup 7}Li and {sup 11}B. Spin-dipole transition strengths in {sup 16}O and neutrino-induced reactions on {sup 16}O are investigated with the new improved Hamiltonian. The Gamow-Teller transition strength in {sup 56}Ni for the new Hamiltonian, which is more fragmented compared to previous calculations, is found to lead to the enhancement of the production yield of {sup 55}Mn in population III stars.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2015

Pushing core-collapse supernovae to explosions in spherical symmetry. I. The model and the case of SN 1987A

We report on a method, PUSH, for artificially triggering core-collapse supernova explosions of massive stars in spherical symmetry. We explore basic explosion properties and calibrate PUSH to reproduce SN 1987A observables. Our simulations are based on the GR hydrodynamics code AGILE combined with the neutrino transport scheme isotropic diffusion source approximation for electron neutrinos and advanced spectral leakage for the heavy flavor neutrinos. To trigger explosions in the otherwise non-exploding simulations, the PUSH method increases the energy deposition in the gain region proportionally to the heavy flavor neutrino fluxes. We explore the progenitor range 18–21 M{sub ⊙}. Our studies reveal a distinction between high compactness (HC; compactness parameter ξ{sub 1.75}>0.45) and low compactness (LC; ξ{sub 1.75}<0.45) progenitor models, where LC models tend to explode earlier, with a lower explosion energy, and with a lower remnant mass. HC models are needed to obtain explosion energies around 1 Bethe, as observed for SN 1987A. However, all the models with sufficiently high explosion energy overproduce {sup 56}Ni and fallback is needed to reproduce the observed nucleosynthesis yields. {sup 57–58}Ni yields depend sensitively on the electron fraction and on the location of the mass cut with respect to the shell structure of the progenitor. We identify a progenitor and a suitable set of parameters that fit the explosion properties of SN 1987A assuming 0.1 M{sub ⊙} of fallback. We predict a neutron star with a gravitational mass of 1.50 M{sub ⊙}. We find correlations between explosion properties and the compactness of the progenitor model in the explored mass range. However, a more complete analysis will require exploring of a larger set of progenitors.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2011

Radioactivity and electron acceleration in supernova remnants

We argue that the decays of radioactive nuclei related to {sup 44}Ti and {sup 56}Ni ejected during supernova explosions can provide a vast pool of mildly relativistic positrons and electrons which are further accelerated to ultrarelativistic energies by reverse and forward shocks. This interesting link between two independent processes - the radioactivity and the particle acceleration - can be a clue for solution of the well known theoretical problem of electron injection in supernova remnants. In the case of the brightest radio source Cas A, we demonstrate that the radioactivity can supply adequate number of energetic electrons and positrons for interpretation of observational data provided that they are stochastically preaccelerated in the upstream regions of the forward and reverse shocks.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2011

AN OFF-AXIS RELATIVISTIC JET MODEL FOR THE TYPE Ic SUPERNOVA SN 2007gr

We propose an off-axis relativistic jet model for the Type Ic supernova SN 2007gr. Most of the energy ({approx}2 x 10{sup 51} erg) in the explosion is contained in non-relativistic ejecta which produces the supernova (SN). The optical emission comes from the decay process of {sup 56}Ni synthesized in the bulk SN ejecta. Only very little energy ({approx}10{sup 48} erg) is contained in the relativistic jet with initial velocity about 0.94 times the speed of light. The radio and X-ray emission comes from this relativistic jet. With some typical parameters of a Wolf-Rayet star (progenitor of Type Ic SN), i.e., the mass-loss rate M-dot =1.0x10{sup -5} M{sub sun} yr{sup -1} and the wind velocity v{sub w} = 1.5 x 10{sup 3} km s{sup -1} together with an observing angle of {theta}{sub obs} = 63.{sup 0}3, we can obtain multiband light curves that fit the observations well. All the observed data are consistent with our model. Thus, we conclude that SN 2007gr contains a weak relativistic jet and we observe the jet from off-axis.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2011

THE FIRST SYSTEMATIC STUDY OF TYPE Ibc SUPERNOVA MULTI-BAND LIGHT CURVES

We present detailed optical photometry for 25 Type Ibc supernovae (SNe Ibc) within d Almost-Equal-To 150 Mpc obtained with the robotic Palomar 60 inch telescope in 2004-2007. This study represents the first uniform, systematic, and statistical sample of multi-band SNe Ibc light curves available to date. We correct the light curves for host galaxy extinction using a new technique based on the photometric color evolution, namely, we show that the (V - R) color of extinction-corrected SNe Ibc at {Delta}t Almost-Equal-To 10 days after V-band maximum is tightly distributed, ((V - R){sub V10}) = 0.26 {+-} 0.06 mag. Using this technique, we find that SNe Ibc typically suffer from significant host galaxy extinction, (E(B - V)) Almost-Equal-To 0.4 mag. A comparison of the extinction-corrected light curves for helium-rich (Type Ib) and helium-poor (Type Ic) SNe reveals that they are statistically indistinguishable, both in luminosity and decline rate. We report peak absolute magnitudes of (M{sub R}) = -17.9 {+-} 0.9 mag and (M{sub R}) = -18.3 {+-} 0.6 mag for SNe Ib and Ic, respectively. Focusing on the broad-lined (BL) SNe Ic, we find that they are more luminous than the normal SNe Ibc sample, (M{sub R}) = -19.0 {+-} 1.1 mag, with a probability of only 1.6% that they are drawn from the same population of explosions. By comparing the peak absolute magnitudes of SNe Ic-BL with those inferred for local engine-driven explosions (GRB-SN 1998bw, XRF-SN 2006aj, and SN 2009bb) we find a 25% probability that relativistic SNe are drawn from the overall SNe Ic-BL population. Finally, we fit analytic models to the light curves to derive typical {sup 56}Ni masses of M{sub Ni} Almost-Equal-To 0.2 and 0.5 M{sub Sun} for SNe Ibc and SNe Ic-BL, respectively. With reasonable assumptions for the photospheric velocities, we further extract kinetic energy and ejecta mass values of M{sub ej} Almost-Equal-To 2 M{sub Sun} and E{sub K} Almost-Equal-To 10{sup 51} erg for SNe Ibc, while for SNe Ic-BL we find higher values, M{sub ej} Almost-Equal-To 5 M{sub Sun} and E{sub K} Almost-Equal-To 10{sup 52} erg. We discuss the implications for the progenitors of SNe Ibc and their relation to those of engine-driven explosions.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

Single-particle spectroscopic factors for spherical nuclei

Within the self-consistent theory of finite Fermi systems, the total single-particle spectroscopic factors for seven doubly magic nuclei of {sup 40}Ca, {sup 48}Ca, {sup 56}Ni, {sup 78}Ni, {sup 100}Sn, {sup 132}Sn, and {sup 208}Pb and for the {sup 188–212}Pb chain of semimagic even lead isotopes are calculated by the energy-density-functional method implemented with a functional in the form proposed by Fayans and his coauthors. The spectroscopic factor is expressed in terms of the Z factor, which is the residue of the single-particle Green’s function at the single-particle pole. The total Z factor calculated in the present study involves both effects of coupling to phonons and the volume Z factor, which is due to the fact that the mass operator features an energy dependence not associated with surface phonons. The volume Z factor is on the same order of magnitude as the phonon-coupling contribution. The volume effect depends only slightly on the nuclear species and on the single-particle state λ. On the contrary, the phonon contribution to the total spectroscopic factor changes upon going over from one state to another and from one nuclear species to another.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2011

Dynamics of nuclear single-particle structure in covariant theory of particle-vibration coupling: From light to superheavy nuclei

The impact of particle-vibration coupling and polarization effects due to deformation and time-odd mean fields on single-particle spectra is studied systematically in doubly magic nuclei from low-mass {sup 56}Ni up to superheavy ones. Particle-vibration coupling is treated fully self-consistently within the framework of the relativistic particle-vibration coupling model. Polarization effects due to deformation and time-odd mean field induced by odd particle are computed within covariant density functional theory. It has been found that among these contributions the coupling to vibrations makes a major impact on the single-particle structure. The impact of particle-vibration coupling and polarization effects on calculated single-particle spectra, the size of the shell gaps, the spin-orbit splittings and the energy splittings in pseudospin doublets is discussed in detail; these physical observables are compared with experiment. Particle-vibration coupling has to be taken into account when model calculations are compared with experiment since this coupling is responsible for observed fragmentation of experimental levels; experimental spectroscopic factors are reasonably well described in model calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗