X-ray Spectra of Young Supernovae

SummaryX-ray spectra of young supernovae (SNe) can provide information on the progenitor star and the interaction of the supernova ejecta and the circumstellar material. I will discuss some examples, with particular emphasis on SN 1998S, whose X-ray spectrum revealed for the first time in a young supernova a wealth of heavy element emission features (Ne, Al, Si, S, Ar, and Fe). By comparison with detailed calculations of supernova explosion elemental yields, these data can be used to constrain the progenitor mass. With increasingly sophisticated models and additional high quality data, application of this technique could result in many more reliable progenitor mass determinations. In addition, high resolution X-ray spectra allow us to measure the temperature evolution of a supernova and can give us a detailed picture of the progenitor’s pre-supernova evolution. As we build up additional examples from the great diversity of core collapse supernovae, we hope to come to a better understanding of the last stages of massive star evolution.

Observations of Type Ia Supernovae and Challenges for Cosmology

SummaryObservations of Type Ia supernovae (SNe Ia) reveal correlations between their luminosities and light-curve shapes, and between their spectral sequence and photometric sequence. Assuming SNe Ia do not evolve at different redshifts, the Hubble diagram of SNe Ia may indicate an accelerating Universe, the signature of a cosmological constant or other forms of dark energy. Several studies raise concerns about the evolution of SNe Ia (e.g., the peculiarity rate, the rise time, and the color of SNe Ia at different redshifts), but all these studies suffer from the difficulties of obtaining high-quality spectroscopy and photometry for SNe Ia at high redshifts. There are also some troubling cases of SNe Ia that provide counter examples to the observed correlations, suggesting that a secondary parameter is necessary to describe the whole SN Ia family. Understanding SNe Ia both observationally and theoretically will be the key to boosting confidence in the SN Ia cosmological results.

Optical Light Curves of Supernovae

SummaryLight curves are the most readily available and most frequently used astrophysical tools for variable phenomena. Supernovae are no exception to this. The information that can be extracted from detailed light and colors curves, together with the detailed study of the spectral evolution, tells us about the progenitor star, the various energy input sources, the explosion environment, material in the line of sight and cosmological effects. Over the past decade we have come to understand the power of detailed light curve studies and how they tie into the exploration of other astrophysical topics.

Two New Possible Mechanisms of Supernova-Like Explosions

SummaryPrimordial black holes (PBHs) of microscopical size can completely absorb neutron stars (NSs) and white dwarfs (WDs) for less than the Hubble time. NS absorption is accompanied by inverse URCA process giving rise to emission of antineutrino. However considerable part of these antineutrino fails to escape NS being drawn into the growing black hole by accreting NS matter. The final stage of dense WD absorption is accompanied by 1051 erg neutrino burst able to ignite nuclear burning giving rise to supernova-like WD explosion.

Supernova Spectra

SummaryIn this paper are summarized the main advances of the last years in the field of SN spectra . The arguments against a monodimensional sequence for SNIa are discussed as well as the efforts to improve the temporal and spectral coverage of this kind of SNe, with the aim to understand the physics of the explosions for their use as cosmological distance indicators. Although variety is the main character of core-collapse SNe, we have been recently surprised by both exceptionally under and over-energetic explosions. The main properties of these two extreme subclasses are here reviewed.

Understanding Type II Supernovae

SummaryWe present the results of a systematic analysis of a group of Type II plateau supernovae that span a large range in luminosities, from faint objects like SN 1997D and 1999br to very luminous events like SN 1992am. The physical properties of the supernovae appear to be related to the plateau luminosity or the expansion velocity. The simultaneous analysis of the observed light curves, line velocities and continuum temperatures leads us to robust estimates of the physical parameters of the ejected envelope. We find strong correlations among several parameters. The implications of these results regarding the nature of the progenitor, the central remnant and the Ni yield are also addressed.

Supernova Statistics

SummaryThe statistics of SN discoveries is used to reveal selection biases of past and current SN searches and to gain insight on the progenitor scenarios for the different SN types. We also report estimates of the SN rate per unit mass in galaxies of different types and on the first attempts to study the evolution of the supernova rate with redshift.

Late Light Curves of Type Ia SNe

SummaryAt late times, the energy deposition in the ejecta of type Ia supernovae is dominated by the slowing of energetic positrons produced in 56Co → 56Fe decays. Through comparisons of simulations of energy deposition in SN Ia models with observed light curves from supernovae, we study the positron transport and thus the magnetic fields of SNe Ia. In this paper, we summarize the current status of these investigations, emphasizing the observations made of two recent SNe Ia, 1999by and 2000cx.

Effects of Small-Scale Fluctuations of Neutrino Flux in Supernova Explosions

SummaryWe examine effects of small-scale fluctuations with angle in the neutrino radiation in core-collapse supernova explosions. As the mode number of fluctuations increases, the results approach those of spherical explosion. We conclude that global anisotropy of the neutrino radiation is the most effective mechanism of increasing the explosion energy when the total neutrino luminosity is given.

VLBI Observations of SN 1979C and SN 1986J

SummaryWe summarize our results on multi-epoch VLBI observations of SN 1979C in the galaxy M100 in Virgo, and of SN 1986 in the galaxy NGC 891. From t = 3.7 to 22 yr after the explosion, SN 1979C expands ∝ tm, almost freely, with m = 0.95 ± 0.03. For a total kinetic energy of 3 × 1051 erg, the expansion result requires a mass-loss to wind-velocity ratio for the progenitor of only 1 × 10−5 M⊙ yr−1per 10 km s−1, an order of magnitude smaller than estimated from radio light-curve fitting. We show a first image with slightly discernible structure of the supernova. For SN 1986J we present five images from 1987 to 2002 and show our result on moderately to strongly decelerated expansion with m = 0.71 ± 0.11. We comment on our result of an inversion of the radio spectrum in terms of the emergence of a possible pulsar nebula.