Radioactivity induced in Apollo 11 lunar surface material by solar flare protons
Solar flare proton induced radioactivity in Apollo 11 lunar surface material compared with stony meteorite data, noting cobalt 56 concentration
Heydegger, H. R.↗
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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↗
The light curve of SN 1987A revisited: constraining production masses of radioactive nuclides
We revisit the evidence for the contribution of the long-lived radioactive nuclides {sup 44}Ti, {sup 55}Fe, {sup 56}Co, {sup 57}Co, and {sup 60}Co to the UVOIR light curve of SN 1987A. We show that the V-band luminosity constitutes a roughly constant fraction of the bolometric luminosity between 900 and 1900 days, and we obtain an approximate bolometric light curve out to 4334 days by scaling the late time V-band data by a constant factor where no bolometric light curve data is available. Considering the five most relevant decay chains starting at {sup 44}Ti, {sup 55}Co, {sup 56}Ni, {sup 57}Ni, and {sup 60}Co, we perform a least squares fit to the constructed composite bolometric light curve. For the nickel isotopes, we obtain best fit values of M({sup 56}Ni) = (7.1 ± 0.3) × 10{sup –2} M {sub ☉} and M({sup 57}Ni) = (4.1 ± 1.8) × 10{sup –3} M {sub ☉}. Our best fit {sup 44}Ti mass is M({sup 44}Ti) = (0.55 ± 0.17) × 10{sup –4} M {sub ☉}, which is in disagreement with the much higher (3.1 ± 0.8) × 10{sup –4} M {sub ☉} recently derived from INTEGRAL observations. The associated uncertainties far exceed the best fit values for {sup 55}Co and {sup 60}Co and, as a result, we only give upper limits on the production masses of M({sup 55}Co) < 7.2 × 10{sup –3} M {sub ☉} and M({sup 60}Co) < 1.7 × 10{sup –4} M {sub ☉}. Furthermore, we find that the leptonic channels in the decay of {sup 57}Co (internal conversion and Auger electrons) are a significant contribution and constitute up to 15.5% of the total luminosity. Consideration of the kinetic energy of these electrons is essential in lowering our best fit nickel isotope production ratio to [{sup 57}Ni/{sup 56}Ni] = 2.5 ± 1.1, which is still somewhat high but is in agreement with gamma-ray observations and model predictions.
79 ASTRONOMY AND ASTROPHYSICS↗
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↗
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↗
Evaluating the purity of a {sup 57}Co flood source by PET
Purpose: Flood sources of {sup 57}Co are commonly used for quality control of gamma cameras. Flood uniformity may be affected by the contaminants {sup 56}Co and {sup 58}Co, which emit higher energy photons. Although vendors specify a maximum combined {sup 56}Co and {sup 58}Co activity, a convenient test for flood source purity that is feasible in a clinical environment would be desirable. Methods: Both {sup 56}Co and {sup 58}Co emit positrons with branching 19.6% and 14.9%, respectively. As is known from {sup 90}Y imaging, a positron emission tomography (PET) scanner is capable of quantitatively imaging very weak positron emission in a high single-photon background. To evaluate this approach, two {sup 57}Co flood sources were scanned with a clinical PET/CT multiple times over a period of months. The {sup 56}Co and {sup 58}Co activity was clearly visible in the reconstructed PET images. Total impurity activity was quantified from the PET images after background subtraction of prompt gamma coincidences. Results: Time-of-flight PET reconstruction was highly beneficial for accurate image quantification. Repeated measurements of the positron-emitting impurities showed excellent agreement with an exponential decay model. For both flood sources studied, the fit parameters indicated a zero intercept and a decay half-life consistent with a mixture of {sup 56}Co and {sup 58}Co. The total impurity activity at the reference date was estimated to be 0.06% and 0.07% for the two sources, which was consistent with the vendor’s specification of <0.12%. Conclusions: The robustness of the repeated measurements and a thorough analysis of the detector corrections and physics suggest that the accuracy is acceptable and that the technique is feasible. Further work is needed to validate the accuracy of this technique with a calibrated high resolution gamma spectrometer as a gold standard, which was not available for this study, and for other PET detector models.
07 ISOTOPE AND RADIATION SOURCES↗
Whimper of a Bang: Documenting the Final Days of the Nearby Type Ia Supernova 2011fe
Using the Hubble Space Telescope (HST) and the Large Binocular Telescope, we followed the evolution of the Type Ia supernova (SN Ia) 2011fe for an unprecedented 1840 days past B-band maximum light and over a factor of 7 million in flux. At 1840 days, the 4000–17000 Å quasi-bolometric luminosity is just (420±20) L{sub ⊙}. By measuring the late-time quasi-bolometric light curve, we present the first confident detection of {sup 57}Co decay in a SN Ia light curve and estimate a mass ratio of log({sup 57}Co/{sup 56}Co)=−1.59{sub −0.07}{sup +0.06}. We do not have a clean detection of {sup 55}Fe, but find a limit of {sup 55}Fe/{sup 57}Co<0.22 with 99% confidence. These abundance ratios provide unique constraints on the progenitor system because the central density of the exploding white dwarf(s) dictates these nucleosynthetic yields. The observed ratios strongly prefer the lower central densities of double-degenerate models ({sup 55}Fe/{sup 57}Co=0.27) over the higher central densities of near-Chandrasekhar-mass single-degenerate models ({sup 55}Fe/{sup 57}Co=0.68). However, additional theoretical studies predicting isotopic yields from a broader range of progenitor systems are motivated by these unique observations. We will continue to observe SN 2011fe for another ∼600 days with HST and possibly beyond.
79 ASTRONOMY AND ASTROPHYSICS↗
The evolution of dust mass in the ejecta of SN 1987A
We present a new analysis of the infrared (IR) emission from the ejecta of SN 1987A covering days 615, 775, 1144, 8515, and 9090 after the explosion. We show that the observations are consistent with the rapid formation of about 0.4 M{sub ⊙} of dust, consisting of mostly silicates (MgSiO{sub 3}), near day 615, and evolving to about 0.45 M{sub ⊙} of composite dust grains consisting of ∼0.4 M{sub ⊙} of silicates and ∼0.05 M{sub ⊙} of amorphous carbon after day ∼8500. The proposed scenario challenges previous claims that dust in supernova (SN) ejecta is predominantly carbon, and that it grew from an initial mass of ∼10{sup −3} M{sub ⊙}, to over 0.5 M{sub ⊙} by cold accretion. It alleviates several problems with previous interpretations of the data: (1) it reconciles the abundances of silicon, magnesium, and carbon with the upper limits imposed by nucleosynthesis calculations, (2) it eliminates the requirement that most of the dust observed around day 9000 grew by cold accretion onto the ∼10{sup −3} M{sub ⊙} of dust previously inferred for days 615 and 775 after the explosion, and (3) establishes the dominance of silicate over carbon dust in the SN ejecta. At early epochs, the IR luminosity of the dust is powered by the radioactive decay of {sup 56}Co, and at late times by at least (1.3–1.6) × 10{sup −4} M{sub ⊙} of {sup 44}Ti.
79 ASTRONOMY AND ASTROPHYSICS↗
VERY LATE PHOTOMETRY OF SN 2011fe
The Type Ia supernova SN 2011fe is one of the closest supernovae of the past decades. Due to its proximity and low dust extinction, this object provides a very rare opportunity to study the extremely late time evolution (>900 days) of thermonuclear supernovae. In this Letter, we present our photometric data of SN 2011fe taken at an unprecedented late epoch of ≈930 days with GMOS-N mounted on the Gemini North telescope (g = 23.43 ± 0.28, r = 24.14 ± 0.14, i = 23.91 ± 0.18, and z = 23.90 ± 0.17) to study the energy production and retention in the ejecta of SN 2011fe. Together with previous measurements by other groups, our result suggests that the optical supernova light curve can still be explained by the full thermalization of the decay positrons of {sup 56}Co. This is in spite of theoretical predicted effects (e.g., infrared catastrophe, positron escape, and dust) that advocate a substantial energy redistribution and/or loss via various processes that result in a more rapid dimming at these very late epochs.
79 ASTRONOMY AND ASTROPHYSICS↗
Beta Decay Study of the T{sub z}=−2{sup 56}Zn Nucleus and the Determination of the Half-Lives of a Few fp-shell Nuclei
This paper concerns the experimental study of the β decay properties of few proton-rich fp-shell nuclei. The nuclei were produced at GANIL in fragmentation reactions, separated with the LISE spectrometer and stopped in an implantation detector surrounded by Ge detectors. The β-delayed gammas, β-delayed protons and the exotic β-delayed gamma-proton emission have been studied. Preliminary results are presented. The decay of the T{sub z}=−2 nucleus {sup 56}Zn has been studied in detail. Information from the β-delayed protons and β-delayed gammas has been used to deduce the decay scheme. The exotic beta-delayed gamma-proton decay has been observed for the first time in the fp-shell. The interpretation of the data was made possible thanks to the detailed knowledge of the mirror Charge Exchange (CE) process and the gamma de-excitation of the states in {sup 56}Co, the mirror nucleus of {sup 56}Cu.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
MULTICOLOR LIGHT CURVE SIMULATIONS OF POPULATION III CORE-COLLAPSE SUPERNOVAE: FROM SHOCK BREAKOUT TO {sup 56}CO DECAY
The properties of the first generation of stars and their supernova (SN) explosions remain unknown due to the lack of actual observations. Recently, many transient surveys have been conducted and the feasibility of detecting supernovae (SNe) of Pop III stars is growing. In this paper, we study the multicolor light curves for a number of metal-free core-collapse SN models (25–100 M{sub ⊙}) to determine the indicators for the detection and identification of first generation SNe. We use mixing-fallback supernova explosion models that explain the observed abundance patterns of metal-poor stars. Numerical calculations of the multicolor light curves are performed using the multigroup radiation hydrodynamic code stella. The calculated light curves of metal-free SNe are compared with non-zero-metallicity models and several observed SNe. We have found that the shock breakout characteristics, the evolution of the photosphere’s velocity, the luminosity, and the duration and color evolution of the plateau, that is, all of the SN phases from shock breakout to {sup 56}Co decay, are helpful for estimating the parameters of the SN progenitor: the mass, the radius, the explosion energy, and the metallicity. We conclude that the multicolor light curves could potentially be used to identify first-generation SNe in current (Subaru/HSC) and future transient surveys (LSST, James Webb Space Telescope). They are also suitable for identifying low-metallicity SNe in the nearby universe (PTF, Pan-STARRS, Gaia).
79 ASTRONOMY AND ASTROPHYSICS↗
PS1-14bj: a hydrogen-poor superluminous supernova with a long rise and slow decay
We present photometry and spectroscopy of PS1-14bj, a hydrogen-poor superluminous supernova (SLSN) at redshift z = 0.5215 discovered in the last months of the Pan-STARRS1 Medium Deep Survey. PS1-14bj stands out because of its extremely slow evolution, with an observed rise of ≳125 rest-frame days, and exponential decline out to ∼250 days past peak at a measured rate of 0.01 mag day{sup −1}, consistent with fully trapped {sup 56}Co decay. This is the longest rise time measured in an SLSN to date, and the first SLSN to show a rise time consistent with pair-instability supernova (PISN) models. Compared to other slowly evolving SLSNe, it is spectroscopically similar to the prototype SN 2007bi at maximum light, although lower in luminosity (L{sub peak}≃4.6×10{sup 43} erg s{sup −1}) and with a flatter peak than previous events. PS1-14bj shows a number of peculiar properties, including a near-constant color temperature for >200 days past peak, and strong emission lines from [O iii] λ5007 and [O iii] λ4363 with a velocity width of ∼3400 km s{sup −1} in its late-time spectra. These both suggest there is a sustained source of heating over very long timescales, and are incompatible with a simple {sup 56}Ni-powered/PISN interpretation. A modified magnetar model including emission leakage at late times can reproduce the light curve, in which case the blue continuum and [O iii] features are interpreted as material heated and ionized by the inner pulsar wind nebula becoming visible at late times. Alternatively, the late-time heating could be due to interaction with a shell of H-poor circumstellar material.
79 ASTRONOMY AND ASTROPHYSICS↗
SN 2010mb: Direct evidence for a supernova interacting with a large amount of hydrogen-free circumstellar material
We present our observations of SN 2010mb, a Type Ic supernova (SN) lacking spectroscopic signatures of H and He. SN 2010mb has a slowly declining light curve (LC) (∼600 days) that cannot be powered by {sup 56}Ni/{sup 56}Co radioactivity, the common energy source for Type Ic SNe. We detect signatures of interaction with hydrogen-free circumstellar material including a blue quasi-continuum and, uniquely, narrow oxygen emission lines that require high densities (∼10{sup 9} cm{sup –3}). From the observed spectra and LC, we estimate that the amount of material involved in the interaction was ∼3 M {sub ☉}. Our observations are in agreement with models of pulsational pair-instability SNe described in the literature.
79 ASTRONOMY AND ASTROPHYSICS↗
GAMMA RAYS FROM TYPE Ia SUPERNOVA SN 2014J
The whole set of INTEGRAL observations of Type Ia supernova SN 2014J, covering the period 19–162 days after the explosion, has been analyzed. For spectral fitting the data are split into early and late periods covering days 19–35 and 50–162, respectively, optimized for {sup 56}Ni and {sup 56}Co lines. As expected for the early period, much of the gamma-ray signal is confined to energies below ∼200 keV, while for the late period it is strongest above 400 keV. In particular, in the late period, {sup 56}Co lines at 847 and 1248 keV are detected at 4.7σ and 4.3σ, respectively. The light curves in several representative energy bands are calculated for the entire period. The resulting spectra and light curves are compared with a subset of models. We confirm our previous finding that the gamma-ray data are broadly consistent with the expectations for canonical one-dimensional models, such as delayed detonation or deflagration models for a near-Chandrasekhar mass white dwarf. Late optical spectra (day 136 after the explosion) show rather symmetric Co and Fe line profiles, suggesting that, unless the viewing angle is special, the distribution of radioactive elements is symmetric in the ejecta.
79 ASTRONOMY AND ASTROPHYSICS↗
SUPERNOVA RESONANCE-SCATTERING LINE PROFILES IN THE ABSENCE OF A PHOTOSPHERE
In supernova (SN) spectroscopy relatively little attention has been given to the properties of optically thick spectral lines in epochs following the photosphere's recession. Most treatments and analyses of post-photospheric optical spectra of SNe assume that forbidden-line emission comprises most if not all spectral features. However, evidence exists that suggests that some spectra exhibit line profiles formed via optically thick resonance-scattering even months or years after the SN explosion. To explore this possibility, we present a geometrical approach to SN spectrum formation based on the 'Elementary Supernova' model, wherein we investigate the characteristics of resonance-scattering in optically thick lines while replacing the photosphere with a transparent central core emitting non-blackbody continuum radiation, akin to the optical continuum provided by decaying {sup 56}Co formed during the explosion. We develop the mathematical framework necessary for solving the radiative transfer equation under these conditions and calculate spectra for both isolated and blended lines. Our comparisons with analogous results from the Elementary Supernova code SYNOW reveal several marked differences in line formation. Most notably, resonance lines in these conditions form P Cygni-like profiles, but the emission peaks and absorption troughs shift redward and blueward, respectively, from the line's rest wavelength by a significant amount, despite the spherically symmetric distribution of the line optical depth in the ejecta. These properties and others that we find in this work could lead to misidentification of lines or misattribution of properties of line-forming material at post-photospheric times in SN optical spectra.
79 ASTRONOMY AND ASTROPHYSICS↗
Wait for it: post-supernova winds driven by delayed radioactive decays
In most astrophysical situations, the radioactive decay of {sup 56}Ni to {sup 56}Co occurs via electron capture with a fixed half-life of 6.1 days. However, this decay rate is significantly slowed when the nuclei are fully ionized because K-shell electrons are unavailable for capture. In this paper, we explore the effect of these delayed decays on white dwarfs (WDs) that may survive Type Ia and Type Iax supernovae (SNe Ia and SNe Iax). The energy released by the delayed radioactive decays of {sup 56}Ni and {sup 56}Co drives a persistent wind from the surviving WD’s surface that contributes to the late-time appearance of these SNe after emission from the bulk of the SN ejecta has faded. We use the stellar evolution code MESA to calculate the hydrodynamic evolution and resulting light curves of these winds. Our post-SN Ia models conflict with late-time observations of SN 2011fe, but uncertainties in our initial conditions prevent us from ruling out the existence of surviving WD donors. Much better agreement with observations is achieved with our models of post-SN Iax bound remnants, providing evidence that these explosions are due to deflagrations in accreting WDs that fail to completely unbind the WDs. Future radiative transfer calculations and wind models utilizing simulations of explosions for more accurate initial conditions will extend our study of radioactively powered winds from post-SN surviving WDs and enable their use as powerful discriminants among the various SN Ia and SN Iax progenitor scenarios.
79 ASTRONOMY AND ASTROPHYSICS↗
SUPER-LUMINOUS TYPE Ic SUPERNOVAE: CATCHING A MAGNETAR BY THE TAIL
We report extensive observational data for five of the lowest redshift Super-Luminous Type Ic Supernovae (SL-SNe Ic) discovered to date, namely, PTF10hgi, SN2011ke, PTF11rks, SN2011kf, and SN2012il. Photometric imaging of the transients at +50 to +230 days after peak combined with host galaxy subtraction reveals a luminous tail phase for four of these SL-SNe. A high-resolution, optical, and near-infrared spectrum from xshooter provides detection of a broad He I {lambda}10830 emission line in the spectrum (+50 days) of SN2012il, revealing that at least some SL-SNe Ic are not completely helium-free. At first sight, the tail luminosity decline rates that we measure are consistent with the radioactive decay of {sup 56}Co, and would require 1-4 M{sub Sun} of {sup 56}Ni to produce the luminosity. These {sup 56}Ni masses cannot be made consistent with the short diffusion times at peak, and indeed are insufficient to power the peak luminosity. We instead favor energy deposition by newborn magnetars as the power source for these objects. A semi-analytical diffusion model with energy input from the spin-down of a magnetar reproduces the extensive light curve data well. The model predictions of ejecta velocities and temperatures which are required are in reasonable agreement with those determined from our observations. We derive magnetar energies of 0.4 {approx}< E(10{sup 51} erg) {approx}< 6.9 and ejecta masses of 2.3 {approx}< M{sub ej}(M{sub Sun }) {approx}< 8.6. The sample of five SL-SNe Ic presented here, combined with SN 2010gx-the best sampled SL-SNe Ic so far-points toward an explosion driven by a magnetar as a viable explanation for all SL-SNe Ic.
79 ASTRONOMY AND ASTROPHYSICS↗
Type IIb supernova 2013df entering into an interaction phase: a link between the progenitor and the mass loss
We report the late-time evolution of Type IIb supernova (SN IIb) 2013df. SN 2013df showed a dramatic change in its spectral features at ∼1 yr after the explosion. Early on it showed typical characteristics shared by SNe IIb/Ib/Ic dominated by metal emission lines, while later on it was dominated by broad and flat-topped Hα and He i emissions. The late-time spectra are strikingly similar to SN IIb 1993J, which is the only previous example clearly showing the same transition. This late-time evolution is fully explained by a change in the energy input from the {sup 56}Co decay to the interaction between the SN ejecta and dense circumstellar matter (CSM). The mass-loss rate is derived to be ∼(5.4±3.2)×10{sup −5} M{sub ⊙} yr{sup −1} (for the wind velocity of ∼20 km s{sup −1}), similar to SN 1993J but larger than SN IIb 2011dh by an order of magnitude. The striking similarity between SNe IIb 2013df and 1993J in the (candidate) progenitors and the CSM environments and the contrast in these natures to SN 2011dh infer that there is a link between the natures of the progenitor and the mass loss: SNe IIb with a more extended progenitor have experienced a much stronger mass loss in the final centuries toward the explosion. It might indicate that SNe IIb from a more extended progenitor are the explosions during a strong binary interaction phase, while those from a less extended progenitor have a delay between the strong binary interaction and the explosion.
79 ASTRONOMY AND ASTROPHYSICS↗