Pair-instability supernova

Abstract: We present photometric observations of an apparent Type Ia supernova (SN Ia) at a redshift of ~1.7, the farthest SN observed to date. The supernova, SN 1997ff, was discovered in a repeat observation by the Hubble Space Telescope (HST) of the Hubble Deep Field-North (HDF-N) and serendipitously monitored with NICMOS on HST throughout the Thompson et al. Guaranteed-Time Observer (GTO) campaign. The SN type can be determined from the host galaxy type: an evolved, red elliptical lacking enough recent star formation to provide a significant population of core-collapse supernovae. The classification is further supported by diagnostics available from the observed colors and temporal behavior of the SN, both of which match a typical SN Ia. The photometric record of the SN includes a dozen flux measurements in the I, J, and H bands spanning 35 days in the observed frame. The redshift derived from the SN photometry, z = 1.7 ± 0.1, is in excellent agreement with the redshift estimate of z = 1.65 ± 0.15 derived from the U300B450V606I814J110J125H160H165Ks photometry of the galaxy. Optical and near-infrared spectra of the host provide a very tentative spectroscopic redshift of 1.755. Fits to observations of the SN provide constraints for the redshift-distance relation of SNe Ia and a powerful test of the current accelerating universe hypothesis. The apparent SN brightness is consistent with that expected in the decelerating phase of the preferred cosmological model, ΩM ≈ 1/3,ΩΛ ≈ . It is inconsistent with gray dust or simple luminosity evolution, candidate astrophysical effects that could mimic previous evidence for an accelerating universe from SNe Ia at z ≈ 0.5. We consider several sources of potential systematic error, including gravitational lensing, supernova misclassification, sample selection bias, and luminosity calibration errors. Currently, none of these effects alone appears likely to challenge our conclusions. Additional SNe Ia at z > 1 will be required to test more exotic alternatives to the accelerating universe hypothesis and to probe the nature of dark energy.

Abstract: The interaction of the outer parts of a supernova envelope with circumstellar matter gives rise to a high-energy density shell. The equation of motion of the shell is deduced based on the approximations that the shell is thin and that the supernova density profile is a power law in radius. The density structure in the shell is Rayleigh-Taylor unstable, and the energy density created by the instability can be a substantial fraction of the original thermal energy density. The instability can drive turbulent motions, and these may amplify the magnetic field and accelerate relativistic electrons. If the efficiency of these processes is comparable to that inferred for the Cassiopeia A supernova remnant, the observed radio luminosity from SN 1980k and SN 1979c can be reproduced. Several mechanisms are considered for the early low-frequency absorption of the radio emission. Free-free absorption by circumstellar matter is the most likely mechanism because of the steep time dependence of the radio emission and the magnitude of the absorption effect. If the circumstellar matter is smoothly distributed, it is inferred that the presupernova star of SN 1980k had a mass loss rate of about 10/sup -5/ M/sub sun/ yr/sup -1/ and that of SN 1979cmore » about 5 x 10/sup -5/ M/sub sun/ yr/sup -1/. Clumping of the matter would reduce the estimated mass loss rates. It is also inferred that SN 1979c had more high velocity matter than did SN 1980k. Thermal X-ray emission is expected from both the shocked circumstellar medium and the shocked supernova matter. The shocked supernova matter dominates the emission in the band observed with the Einstein Observatory, and it can produce the X-ray flux observed from SN 1980k. Inverse Compton emission is another possibility for the observed X-ray emission, but it is less likely because it would decrease the number of radio-emitting electrons. Subject headings: nebulae: supernova remnants: radiation mechanisms: radio sources: general: X-rays: sources« less

Abstract: We calculate nucleosynthesis in core collapse explosions of massive Population III stars and compare the results with abundances of metal-poor halo stars to constrain the parameters of Population III supernovae. We focus on iron peak elements, and, in particular, we try to reproduce the large [Zn/Fe] observed in extremely metal-poor stars. The interesting trends of the observed ratios [Zn, Co, Mn, Cr, V/Fe] can be related to the variation of the relative mass of the complete and incomplete Si-burning regions in supernova ejecta. We find that [Zn/Fe] is larger for deeper mass cuts, smaller neutron excess, and larger explosion energies. The large [Zn/Fe] and [O/Fe] observed in the very metal-poor halo stars suggest deep mixing of complete Si-burning material and a significant amount of fallback in Type II supernovae. Furthermore, large explosion energies (E51 2 for M ~ 13 M☉ and E51 20 for M 20 M☉) are required to reproduce [Zn/Fe] ~ 0.5. The observed trends of the abundance ratios among the iron peak elements are better explained with this high-energy (hypernova) model than with the simple deep mass cut effect because the overabundance of Ni can be avoided in the hypernova models. We also present the yields of pair instability supernova explosions of M 130-300 M☉ stars and discuss that the abundance features of very metal-poor stars cannot be explained by pair instability supernovae.

Abstract: Nucleosynthesis, light curves, explosion energies, and remnant masses are calculated for a grid of supernovae resulting from massive stars with solar metallicity and masses from 9.0 to 120 solar masses. The full evolution is followed using an adaptive reaction network of up to 2000 nuclei. A novel aspect of the survey is the use of a one-dimensional neutrino transport model for the explosion. This explosion model has been calibrated to give the observed energy for SN 1987A, using several standard progenitors, and for the Crab supernova using a 9.6 solar mass progenitor. As a result of using a calibrated central engine, the final kinetic energy of the supernova is variable and sensitive to the structure of the presupernova star. Many progenitors with extended core structures do not explode, but become black holes, and the masses of exploding stars do not form a simply connected set. The resulting nucleosynthesis agrees reasonably well with the sun provided that a reasonable contribution from Type Ia supernovae is also allowed, but with a deficiency of light s-process isotopes. The resulting neutron star IMF has a mean gravitational mass near 1.4 solar masses. The average black hole mass is about 9 solar masses if only the helium core implodes, and 14 solar masses if the entire presupernova star collapses. Only ~10% of supernovae come from stars over 20 solar masses and some of these are Type Ib or Ic. Some useful systematics of Type IIp light curves are explored.