The mechanism of supernova Ia explosion in elliptical galaxies

Recent observational data on the type Ia supernova rates are in excellent agreement with the earlier results of the population synthesis of binary stars and confirm that the overwhelming majority of type Ia supernovas (～99%) in elliptical galaxies form via mergers of binary white dwarfs with a total mass exceeding the Chandrasekhar limit.     

The impact of a supernova explosion in a very massive binary

We consider the effect of a supernova (SN) explosion in a very massive binary that is expected to form in a portion of Population III stars with the mass higher than  100 M_⊙  . In a Population III binary system, a more massive star can result in the formation of a black hole (BH) and a surrounding accretion disc. Such BH accretion could be a significant source of the cosmic reionization in the early Universe. However, a less massive companion star evolves belatedly and eventually undergoes a SN explosion, so that the accretion disc around a BH might be blown off in a lifetime of companion star. In this paper, we explore the dynamical impact of a SN explosion on an accretion disc around a massive BH, and elucidate whether the BH accretion disc is totally demolished or not. For the purpose, we perform three-dimensional hydrodynamic simulations of a very massive binary system, where we assume a BH of  10³ M_⊙  that results from a direct collapse of a very massive star and a companion star of  100 M_⊙  that undergoes a SN explosion. We calculate the remaining mass of a BH accretion disc as a function of time. As a result, it is found that a significant portion of gas disc can survive through three-dimensional geometrical effects even after the SN explosion of a companion star. Even if the SN explosion energy is higher by two orders of magnitude than the binding energy of gas disc, about a half of disc can be left over. The results imply that the Population III BH accretion disc can be a long-lived luminous source, and therefore could be an important ionizing source in the early Universe.     

An earlier explosion date for the Crab Nebula supernova

The Chinese first reported the Crab Nebula supernova on 1054 July 5. Ecclesiastical documents from the near east reported it in April and May of 1054. More than 33 petroglyphs made by Native Americans in the US and Mexico are consistent with sightings both before and after conjunction with the Sun on 1054 May 27. We found a petroglyph showing the new star close to Venus and the Moon, which occurred on 1054 April 12 and April 13, respectively. Collins et al., using the four historical dates, derived a light curve that is like that of a Type Ia supernova. The only remaining problem with this identification is that this supernova was near maximum light for 85 d, which is unlike the behavior of any known supernova.     

The supernova fragmentation model of solar system formation

We have further developed Brown's model of solar system formation. In this model, each fragment of an ejected supernova shell evolves into a separate solar system. Specifically, we have formulated the reverse-flow hypothesis that may be responsible for the inner, earthlike planets. We have written a computer program with which it is possible to calculate mass distributions within a solar nebula. We have found mass distributions similar to our solar system over a wide range of the model parameters.Los Alamos National Laboratory is operated by the University of California for the U.S. Dept. of Energy under contract W-7405-ENG-36.     

A simple model of a supernova

In this paper we formulate the problem of the collapse of a spherically-symmetric, radiating body in general relativity. The requirement that the metric and its normal derivative be continuous across the boundary imposes conditions upon the evolution of the star and allows identification of physical phenomena measured by a distant observer. A solution to Einstein's field equations for the exterior of a spherically-symmetric radiating body is that derived originally by Vaidya in 1951. By requiring the continuity described above we identify the mass, luminosity, velocity, and time increment measured by a distant observer in terms of the metric parameters evaluated in a frame comoving with the outer boundary. We also assume that the interior metric is a sum of products of functions of the radius and time. The continuity requirements allow the evolution of two of the three functions of time to be determined. The evolution of the third function, describing the motion of the core, is determined by the imposition of an equation of state at the center. The adiabatic index derived from the Baym-Bethe-Pethick equation of state was used to provide this last equation. A major result is obtaining an analytic solution to Einstein's field equations describing the core of a collapsing star. As a consequence of this solution we found that for the relatively small values of the adiabatic index (_max1.6), the star smoothly made the transition to a final collapsed state. Neither bounce nor shock wave was obtained. Also, there is a readily understood connection between the adiabatic index, and such parameters of the edge of the core as the velocity and acceleration. Finally, the analytic solutions provide the time-scales for the collapse which are significantly different from that of free-fall. The retarding effects of pressure upon the collapse are apparent. It is hoped that such analytic solutions will provide insight into more complicated dynamic systems in general relativity.     

A self-similar solution for a supernova explosion with allowance for accelerated relativistic particles

A self-similar solution to Sedov’s problem of a strong explosion in a homogeneous medium is generalized to the case of relativistic-particle generation in a supernova remnant; the particles are accelerated by Fermi’s mechanism at the shock front and in the perturbed post-shock region. Self-similarity takes place if the thickness of the prefront is small compared to its radius and if the pressure ratio of the relativistic and nonrelativistic components at the shock front is kept constant. In the presence of relativistic particles, the time dependence of the shock-front radius remains the same as that in their absence, but the plasma parameters in the inner perturbed region change appreciably. The shell of the matter raked up by the explosion is denser and thinner than that in the nonrelativistic case, the relativistic-particle pressure in the central region remains finite, and the nonrelativistic-gas pressure at the explosion center approaches zero. The influence of relativistic particles on the transition to the radiative phase of expansion of the supernova remnant and on its dynamics is studied. It is shown that relativistic particles can decrease several-fold the remnant radius at which the transition to the radiative phase occurs.     

Hints of a second explosion(a quark nova) in Cassiopeia A supernova

We show that the explosive transition of the neutron star(NS)to a quark star(QS)(a Quark Nova)in Cassiopeia A(Cas A)a few days following the supernova(SN)proper can account for several of the puzzling kinematic and nucleosynthetic features that are observed.The observed decoupling between Fe and44Ti and the lack of Fe emission within44Ti regions is expected in the QN model owing to the spallation of the inner SN ejecta by relativistic QN neutrons.Our model predicts the44Ti to be more prominent to the NW of the central compact object(CCO)than in the SE and little of it along the NE-SW jets,in agreement with Nu Star observations.Other intriguing features of Cas A are addressed,such as the lack of a pulsar wind nebula and the reported few percent drop in the CCO temperature over a period of 10 yr.     

A model of supernova feedback in galaxy formation

A model of supernova feedback during disc galaxy formation is developed. The model incorporates infall of cooling gas from a halo, and outflow of hot gas from a multiphase interstellar medium (ISM). The star formation rate is determined by balancing the energy dissipated in collisions between cold gas clouds with that supplied by supernovae in a disc marginally unstable to axisymmetric instabilities. Hot gas is created by thermal evaporation of cold gas clouds in supernova remnants, and criteria are derived to estimate the characteristic temperature and density of the hot component and hence the net mass outflow rate. A number of refinements of the model are investigated, including a simple model of a galactic fountain, the response of the cold component to the pressure of the hot gas, pressure-induced star formation and chemical evolution. The main conclusion of this paper is that low rates of star formation can expel a large fraction of the gas from a dwarf galaxy. For example, a galaxy with circular speed 50 km s¹ can expel 6080 per cent of its gas over a time-scale of 1 Gyr, with a star formation rate that never exceeds 0.1 M yr¹. Effective feedback can therefore take place in a quiescent mode and does not require strong bursts of star formation. Even a large galaxy, such as the Milky Way, might have lost as much as 20 per cent of its mass in a supernova-driven wind. The models developed here suggest that dwarf galaxies at high redshifts will have low average star formation rates and may contain extended gaseous discs of largely unprocessed gas. Such extended gaseous discs might explain the numbers, metallicities and metallicity dispersions of damped Lyman systems.     

The next galactic supernova

It is pointed out that there is a better than even chance that a galactic supernova will occur during the lifetime of the present generation of astronomers. A brief discussion is given of a number of types of observations that could be made of such a unique event. It would be particularly important to obtain speckle interferometry of the expanding supernova. High time-resolution spectroscopy and photometry should be obtained during the early phases of the outburst.     

The nearby supernova factory

The Nearby Supernova Factory is an international project dedicated to the study of the nearby thermonuclear (type Ia) supernovæ. Based upon the NEAT search for the target discovery and the dedicated integral field spectrograph SNIFS for the follow‐up, the goal is to study, over a continuous period of 4 years, the spectro‐photometric evolution of ∼300 SNe Ia at z < 0.08 from −15 to +50 days in the extended optical range (320–1000 nm). This will allow to probe in detail the local Hubble diagram, SNe Ia physics and the SNe‐host galaxy correlations, serving as an unprecedented nearby benchmark for the high‐z cosmological studies to come. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dependence of the acceleration of the outer edge of a stellar envelope on supernova explosion energy

Based on numerical simulations of a supernova explosion, we investigate the shock-wave breakout through the stellar surface. The computations have been performed in a wide range of explosion energies and presupernova masses. The results are compared with the classical Gandelman-Frank-Kamenetsky self-similar solution. We have determined the dependence of an arbitrary coefficient in the self-similar solution on the explosion energy and presupernova structure. The derived analytical approximation formula for this coefficient can be used to estimate the supernova explosion energy from such parameters of the ejected envelope determined from astronomical observations as its maximum expansion velocity and the density distribution along its outer edge. The formula may prove to be also useful in studying the X-ray and gamma-ray bursts that accompany the shock-wave breakout through the surface of compact presupernovae.     

The evolution of supernova remnants

The observational data analysis is based on the selection of 14 shell-type SNR, whose distances are quite reliable. Parameters of those SNR characterizing the values of the mean electron densityn _e, the change ofk ^2/7 H and velocity of expansionV are taken. The other parameters of SNR, such as energy of explosion, energy in magnetic field, and relativistic particles, and its increase during the expansion of SNR, are taken and analysed.     

Extinction correction for Type Ia supernova rates – I. The model

In this paper, we present and discuss a new Monte Carlo approach aimed at correcting the observed supernova (SN) rates for the effects of host galaxy dust extinction. The problem is addressed in a general way and the model includes SN position distributions, SN light-curve and spectral library and dust properties and distribution as input ingredients. Even though the recipe we propose is in principle applicable to all SN types, in this paper, we illustrate the use of our model only for Type Ia. These represent, in fact, the simplest test case, basically due to their spectroscopic homogeneity, which to a first approximation allows one to treat them all in the same way. This test case shows that the final results do not depend critically on the spiral arm dust geometry, while the total amount of dust, its properties and the size of the Galactic bulge do have a strong effect. With the availability of more complete spectral libraries and a more accurate knowledge of SN spatial distribution, the method we propose here can be easily extended to core collapse events.     

The fading of supernova 1997D

We present a new set of spectroscopic and photometric data extending the observations of SN 1997D to over 400 d after the explosion. These observations confirm the peculiar properties of SN 1997D, such as the very low abundance of ⁵⁶Co (0.002 M_⊙) and the low expansion velocity of the ejecta (∼1000 km s⁻¹). We discuss the implications of these observations for the character of the progenitor and the nature of the remnant, showing that a Crab-like pulsar or an accreting neutron star formed in the explosion of a low-mass progenitor should already have produced a detectable luminosity at this epoch, in contrast with photometric data. On the other hand, the explosion of a high-mass progenitor with the formation of a black hole is consistent with the available observations. The consequences of this conclusion regarding the nature of the explosion and the prospects of directly identifying the black hole are also addressed.     

The unusual supernova 1987A

V andB light curves for supernova 1987A covering some 120 days from the outburst are here presented and discussed; they are shown to be rather atypical for a type II supernova. The absolute magnitude at maximum brightness is also analyzed, and after applying a correction for interstellar absorption we obtainM _{V, max, 0} =–16.1, andM _{B, max, 0} =–14.7; is is then concluded that 1987A is a supernova quite fainter than average. A comparison with other known supernova is made and some similarity is found with peculiar objects such as 1948B in NGC 6946, and probably, 1909 A in M 101.Research supported in part by SECyT and CONICOR.     

A simple shock wave model of supernova remnant IC 443

This paper contains a model of supernova remnant IC 443 and the interstellar gas surrounding it. The basis of this model is the analysis of the motion of non-spherical adiabatic shock waves due to Kompaneets (1960). Observations of adjacent Hi and Hii regions have been used by several authors to determine the density of gas in the neighbourhood of IC 443. The model gives for the explosion energy and age of IC 443, 1.8×10⁵⁰ erg and 13 000 yr, respectively. The expansion velocity of IC 443 using the present model is in reasonabel agreement with observations of the remnant.     

A magnetohydrodynamic model of whistler duct structure in the magnetosphere

In this study, the physical structure for the propagation of whistler waves within a duct in the Earth's magnetosphere is investigated by means of magnetohydrodynamic (MHD) theory. Expressions for the current density and induced magnetic field are determined analytically and evaluated in terms of two models for the duct plasma density distribution. It is found that once the duct is formed, forces associated with the current structure will maintain it. MHD instabilities are examined briefly and found to be unlikely to threaten duct maintenance in regions where whistlers are typically observed. Examination of some effects of field-aligned currents suggest that this may be a viable mechanism for duct formation.     

Self-similar model of magnetohydrodynamic radiative shock waves with increasing density

The magnetohydrodynamic model of shock waves has been discussed in an atmosphere with gravitation and radiation. The disturbance is headed by a strong shock of increasing density. The medium ahead of the shock is assumed to be inhomogeneous and at rest. Variation of magnetic field radiation flux, and other flow variables are given in tabular form.     

Cylindrical magnetohydrodynamic model of shock waves with radiation heat flux

Similarity solutions have been obtained for a cylindrical piston advancing with constant speed into a uniform plasma of infinite electrical conductivity and uniform axial magnetic field with heat radiation. The total energy of the expanding wave has been supposed to remain constant. The plasma is assumed to be a perfect grey gas in local thermodynamic equilibrium. To make the discussions less complicated the simplifying assumptions include transparent shock, cool piston neither an emitter nor a reflector and negligible radiation pressure and energy.This research was partially supported by a grant from U.G.C., India.