IUE observations of supernova remnants

Ultraviolet spectra of supernova remnants obtained with the IUE satellite provide unique information concerning the shock conditions and elemental abundances in the optically bright filaments. High temperature species such as N V provide diagnostics for shock velocities above 100 km s^?1, and strong lines of carbon and silicon in the IUE spectral range make it possible to study the destruction of refractory grains in shocked interstellar gas. Observations of a non-radiative shock at the edge of the Cygnus Loop provide constraints on the physics of the shock front itself. Most of the very young remnants whose optical spectra show anomalous elemental abundances are too highly reddened for IUE observations, but extensive observations of the Crab Nebula and a spectrum of the supernova remnant in NGC 4449 yield carbon to oxygen ratios from which the mass of the progenitor may be estimated.     

VHE Gamma-ray supernova remnants

Increasing observational evidence gathered especially in X-rays and γ-rays during the course of the last few years support the notion that Supernova remnants (SNRs) are Galactic particle accelerators up to energies close to the “knee” in the energy spectrum of Cosmic rays. This review summarises the current status of γ-ray observations of SNRs. Shell-type as well as plerionic type SNRs are addressed and prospect for observations of these two source classes with the upcoming GLAST satellite in the energy regime above 100 MeV are given.     

X-ray synchrotron emission from supernova remnants

X-ray synchrotron emission tells us of the highest energy reached by accelerated electrons. In a few supernova remnants (SN 1006, G347.3-0.5) this is the dominant form of X-ray radiation, but in most it is superposed to the dominant thermal emission. Thanks to the spectro-imaging capability of Chandra and XMM-Newton, X-ray synchrotron emission has now been unambiguously detected in most young supernova remnants (Cas A, Tycho, Kepler). It arises in a very thin shell (a few arcsecs) at the blast wave. The thinness of that shell (much broader in the radio domain) implies that the high energy electrons cool down very fast behind the shock. The magnetic field that one deduces from that constraint is more than 100 μG behind the shock.     

X-ray emission from supernova remnants observed with ROSAT

Spectrally resolved X-ray images of galactic supernova remnants have been obtained both from the ROSAT all-sky survey and a number of pointed observations. There is substantial evidence for significant spatial variation in temperature, density and pressure across the older, thermal remnants like the Vela SNR, the Cygnus Loop and the North Polar Spur. Both the brightness distribution and the pressure variations observed point towards recently shocked interstellar clouds and filaments, which dominate the X-ray emission pattern. Across the Puppis-A SNR an arc-shaped absorption structure has been detected, which is demonstrated to be produced by cold gas located close to the shock front of the Vela SNR. Across IC443 a similar absorption pattern has been observed, which is created by a cold shell associated with a previously unknown, ROSAT discovered SNR, which lies in front of IC443. Finally, a statistically overview of the SNRs detected in the ROSAT all-sky survey is presented. About half of the catalogued radio remnants have been observed in the survey and another 90 sources have been found which are considered to be candidates of new SNRs.     

Einstein observations of hot stars

Surveys with instruments on the $\text{Einstein Observatory}$ have shown that essentially all 0 and B main sequence stars are X-ray sources as are many, if not all, 0B supergiants and Wolf-Rayet stars. The X-ray luminosities are sufficient to explain broad lines from the superionization stages seen in the UV spectra of the stars. High energy resolution spectra from the Solid State Spectrometer are shown to place severe constraints on various models for the location of the X-ray sources in the outer atmospheres of the stars. Coronal and embedded shock models for the X-ray emission are discussed and each is found to have some problems in explaining the X-ray emission of 0B stars. X-ray line emission of Si XIII and S XV in ? Ori is discussed and interpreted as arising from magnetically confined loops.     

Einstein observations of cool stars

Observations of cool stars with the $\text{Einstein}$ Observatory (HEAO-2) have brought about a fundamental change in our knowledge and understanding of stellar coronae. The existence of X-ray emission from stars throughout the H-R diagram, the wide range of X-ray luminosity within a given spectral and luminosity class, and the strong correlation of X-ray luminosity with stellar age and rotation are among the more significant $\text{Einstein}$ results. These results are strong evidence for the influence of stellar dynamo action on the formation and heating of stellar coronae. A discussion of relevant consortium and guest observations will be given. The Hyades cluster, in particular, will serve as an example to demonstrate the usefulness of X-ray observations in the study of stellar activity and coronal evolution.     

Evolution of magnetic fields and cosmic ray acceleration in supernova remnants

Observations show that the magnetic field in young supernova remnants (SNRs) is significantly stronger than can be expected from the compression of the circumstellar medium (CSM) by a factor of four expected for strong blast waves. Additionally, the polarization is mainly radial, which is also contrary to expectation from compression of the CSM magnetic field. Cosmic rays (CRs) may help to explain these two observed features. They can increase the compression ratio to factors well over those of regular strong shocks by adding a relativistic plasma component to the pressure, and by draining the shock of energy when CRs escape from the region. The higher compression ratio will also allow for the contact discontinuity, which is subject to the Rayleigh–Taylor (R–T) instability, to reach much further out to the forward shock. This could create a preferred radial polarization of the magnetic field. With an Adaptive Mesh Refinement MHD code (AMRVAC), we simulate the evolution of SNRs with three different configurations of the initial CSM magnetic field, and look at two different equations of state in order to look at the possible influence of a CR plasma component. The spectrum of CRs can be simulated using test particles, of which we also show some preliminary results that agree well with available analytical solutions.     

Electron–ion temperature equilibration at collisionless shocks in supernova remnants

The topic of this review is the current state of our knowledge about the degree of initial equilibration between electrons, protons and ions at supernova remnant (SNR) shocks. Specifically, the question has been raised as to whether there is an inverse relationship between the shock velocity and the equilibration. This review aims to compile every method that has been used to measure the equilibration and every SNR on which they have been tested. I review each method, its problems and uncertainties and how those would effect the degree of equilibration (or velocity) inferred. The final compilation of observed electron to proton temperature ratios as a function of shock velocity gives an accurate, conservative picture of the state of our knowledge and the avenues we need to pursue to make progress in our understanding of the relation between the velocity of a shock and the degree of equilibration.     

Cosmic-ray composition and its relation to shock acceleration by supernova remnants

An overview is given on the present status of the understanding of the origin of galactic cosmic rays. Recent measurements of charged cosmic rays and photons are reviewed. Their impact on the contemporary knowledge about the sources and acceleration mechanisms of cosmic rays and their propagation through the Galaxy is discussed. Possible reasons for the knee in the energy spectrum and scenarios for the end of the galactic cosmic-ray component are described.     

Einstein X-ray observations of cataclysmic variables

Observations with the imaging X-ray detectors on the Einstein Observatory have led to a large increase in the number of low luminosity X-ray sources known to be associated with cataclysmic variable stars (CVs). The high sensitivity of the Einstein instrumentation has permitted study of their short timescale variability and spectra. The data are adding significantly to our knowledge of the accretion process in cataclysmic variables and forcing some revision in our ideas concerning the origin of the optical variability in these stars.     

IUE and Einstein observations of supernovae

In this paper IUE observations of two type II and three type I Supernovae (see Table I and Table II) are reviewed. The type II events were also observed by Einstein and SN 1980k was detected in the soft X-ray energy band. Combining UV spectra available of the same events one has the elements to construct a physical picture which accounts for all observations. For the type II events it appears that the progenitor star was a massive supergiant which underwent a severe mass loss before becoming Supernova. For the type I events there is neither X-ray nor, for the time being, radio detection. The high similarity of the optical and UV spectra for the three events indicates that type I Supernovae are the end products of one and the same phenomenon.     

Einstein X-ray observations of clusters of galaxies

The X-ray imaging capability of the Einstein Observatory has provided new observational material in many branches of astrophysics. In this contribution we will review the implications of the X-ray observations for the classification of clusters, the formation of SO galaxies, and the interaction of the galaxies with the intracluster gas.     

Exosat observations of the supernova remnant cas a

The young supernova remnant Cas A has been observed with the imaging proportional counter (PSD) of the EXOSAT observatory. High quality spatially resolved, spectral data allow for the first time the determination of the temperature structure of the remnant. Preliminary results on the distribution of temperature and emission measureover the remnant are presented.     

Einstein observations of high luminosity X-ray binaries

Recent observational advances in the study of high luminosity x-ray binaries have permitted investigation of the interaction of the outgoing x-radiation with the accreting matter surrounding the compact object. In two sources, 4U1822-37 and 4U2129+47, extended EINSTEIN coverage has led to the detection of partial x-ray eclipses, which indicate that the x-ray emitting regions must be extended in size. These have been interpreted as evidence for a large Compton-thick corona produced by evaporation of cool material off the surface of an accretion disk. In three other sources, 4U1915-05, 4U1624-49, and Cygnus X-2, evidence has been found for short x-ray absorption dips which are likely to be associated with obscuration by cool dense matter at the outer edge of the disk. In 4U1915-05, these dips are strictly periodic and determine the binary period for the system. In Cygnus X-2, the dips appear to be quasiperiodic, while in 4U1624-49, insufficient coverage has prevented clarification of the temporal properties of the absorption.For the brightest cosmic x-ray source, Scorpius X-1, the EINSTEIN objective grating spectrometer has provided high resolution spectra (λ/Δλ ～50) in the wavelength range 40-10 Å. The spectra reveal absorption features due to intervening helium, nitrogen, and oxygen. The implied nitrogen and oxygen abundances are anomalous and suggest that the absorbing material is intrinsic accreting matter which has been transferred from the surface of an evolved companion. Constraints on the inclination of the system then imply that this cool dense material must be well out of the orbital plane of the binary.     

Coronal X-ray temperatures from Einstein and EXOSAT observations

Spectral analysis of coronal X-ray emission from stars observed with both the Einstein and EXOSAT Observatories is presented. Using computer codes developed by Raymond and Smith /1/ and Landini and Fossi /2/ to calculate the X-ray emission from optically thin plasma in collisional equilibrium we find that the derived coronal parameters depend only rather insensitively on the details of the calculated theoretical X-ray spectrum and demonstrate how both the Einstein Observatory IPC spectra and the EXOSAT LE filter ratios can be naturally and simultaneously explained by assuming an underlying continuous emission measure distribution as is the case in the solar corona.     

A model grid for the spectral analysis of X-ray emission in young Type Ia supernova remnants

We address a new set of models for the spectral analysis of the X-ray emission from young, ejecta-dominated Type Ia supernova remnants. These models are based on hydrodynamic simulations of the interaction between Type Ia supernova explosion models and the surrounding ambient medium, coupled to self-consistent ionization and electron heating calculations in the shocked supernova ejecta, and the generation of synthetic spectra with an appropriate spectral code. The details are provided elsewhere, but in this paper we concentrate on a specific class of Type Ia explosion models (delayed detonations), commenting on the differences that arise between their synthetic X-ray spectra under a variety of conditions.     

Radio continuum observations of the galactic supernova remnant Vela Z (G266.2-1.2)

We present multi frequency radio-continuum observations of Galactic SNR Vela Z (G266.2-1.2), associated with the prominent X-ray source RX J0852.0-4622 discovered in 1998. Our study of this Galactic supernova remnant (SNR) is based on low-resolution mosaic observations with the ATCA radio interferometer at 1384 and 2496 MHz, Parkes 4850 MHz and MOST 843 MHz survey data. We determine the radio spectral index for the most prominent features of this SNR and compare these features with X-ray observations. We note a sudden spectral turnover at higher then expected frequencies of ∼1384 MHz.     

Cosmic ray acceleration by supernova shocks

We analyse the results of recent measurements of nonthermal emission from individual supernova remnants (SNRs) and their correspondence to the nonlinear kinetic theory of cosmic ray (CR) acceleration in SNRs. It is shown that the theory fits these data in a satisfactory way and provides the strong evidences for the efficient CR production in SNRs accompanied by significant magnetic field amplification. Magnetic field amplification leads to considerable increase of CR maximum energy so that the spectrum of CRs accelerated in SNRs is consistent with the requirements for the formation of Galactic CR spectrum up to the energy ∼10¹⁷ eV.     

Prospects for observing dark-matter remnants with GLAST

The satellite-based experiment, GLAST (Gamma-ray Large Area Space Telescope), is under construction and is planned to measure the cosmic γ-ray flux in the energy range 20 MeV to >300 GeV, with supporting measurements for γ-ray bursts from 10 keV to 25 MeV. With its launch in 2007, GLAST will open a new and important window on a wide variety of high-energy phenomena, including exotic relics from the Big Bang. Among these may be the decay/annihilation products of the hypothesized super symmetric image of the known particles. Single-photon energy thresholds for channels leading to such final states have been excluded in a model-dependent manner by accelerator searches to energies greater than 50 GeV. The ability of GLAST to set limits on this important component of cosmological evolution is presented along with an update on the present status of this mission.