The elemental abundances of the Crab Nebula are compared with the presupernova models of 8–12 M⊙ stars. The small carbon abundance of the Crab is consistent with only the star whose main-sequence mass was 8–9.5 M⊙. More massive stars contain too much carbon in the helium layer and smaller mass stars do not leave neutron stars. A scenario for the Crab Nebula's progenitor is proposed.

Using deeply exposed Schmidt plates, van den Bergh (1970) discovered a peculiar jetlike feature extending about 100″ beyond the Crab Nebula's northern boundary. The feature roughly coincided with a spur in the outer intensity contour map of the Crab's continuum emission (5200–6400A) made by Woltjer (1957) from plates taken by Baade with the 200 inch. However, little if any continuous synchroton emission is visible in the jet's region on Scargle's (1970) deep continuum photograph. More recent imaging of the jet by Chevalier and Gull (1975) and Wyckoff et al. (1976) using narrow passband interference-filters, show it slightly better than van den Bergh's plates, and indicate it is most visible in [0 III] 5007A emission. Spectroscopy of the jet's southern portion by Davidson (1978, 1979) confirmed that the [0 III] 4959A, 5007A lines are the brightest optical emissions in the jet and suggested a low radial velocity of about 100 km s−1

Detailed stationary photoionization models with homogeneous chemical composition were constructed for a bright filament of the Crab Nebula centered ~42″ W-SW of the pulsar. So far this filament is the only one which has been observed in the ultraviolet (Davidson et al, 1982), in the visual (Miller, 1978; Davidson et al, 1982) and in the near-infrared (Dennefeld and Péquignot, 1982), so that numerous constraints and meaningful tests of the models exist. On the other hand the computer program used in the calculations includes recently introduced atomic physics processes (charge exchange reactions and “low-temperature” di-electronic recombinations) and was tested and calibrated by means of models of the high-excitation planetary nebula NGC 7027 whose line spectrum shares some characteristics with that of the Crab Nebula.

A high resolution X-ray image from the Einstein Observatory of the young supernova remnant G292.0+1.8 (MSH11–54), previously noted as peculiar in terms of its spectral and morphological properties at optical and radio wavelengths, also shows an unusual X-ray morphology. Instead of a limb-brightened X-ray shell characteristic of most SNRs, the remnant consists of a central bar-like feature superposed on an ellipsoidal disc of approximately uniform surface brightness. We attribute the bar emission to a ring of oxygen-rich material ejected in the equatorial plane of a massive rotating progenitor, and the uniform disc component to emission from material with roughly cosmic composition heated by the accompanying blast wave. This interpretation provides observational support for the rotating precursor model of a Type II supernova discussed by Bodenheimer and Woosley.

Optical velocity field mapping of G292.0+1.8 in the [0III] λ5007 å line has been carried out using the IPCS with the 3.6 m ESO telescope at La Silla. Our data are not consistent with the suggestion that the [0III] emitting material in the western portion of this remnant is concentrated in an expanding ring. The existing data on G292.0+1.8 suggests that only the brightest portion of a thick shell of ejecta with high velocity spurs is observed. The expansion centroid, size, velocity and age of this SNR are derived.

We present a velocity map of the young oxygen-rich supernova remnant (1E0102.2–7219) in the Small Magellanic Cloud, obtained with the Anglo-Australian Telescope. The velocity structure is complex, and implies a high degree of asymmetry during the Type II supernova explosion. Our data can be modelled geometrically in terms of a severely distorted ring of oxygen-rich ejecta. This result, together with the evidence for expanding rings in similar remnants, suggests non-spherical ejection to be an intrinsic characteristic of Type II supernovae. We have also obtained two-dimensional spectroscopy of the diffuse halo of emission which partially surrounds 1E0102.2–7219. The halo exhibits the high excitation line of HeII λ4686, and is either a fossil HII region created by a UV flash accompanying the supernova, or alternately, is being excited by intense UV radiation from the remnant itself. It is the first clear association of a high excitation region with a supernova remnant.

Three supernovae have so far been detected in the radio range shortly after their optical outbursts. All are Type IIs. A fourth supernova, a Type I, is being monitored for radio emission but, at an age of approximately one year, has not yet been detected. For two of the supernovae, extensive data are presented on their “light curves” and spectra and models which have been suggested in the literature are discussed.

Radio and X-ray observations of SN 1979c and SN 1980k offer a unique opportunity of monitoring the transition from supernovae to remnants. By means of the two-frequency radio light curves, we test the hypothesis that these objects are surrounded by circumstellar matter, originated in a pre supernova wind, and derive the relevant parameters. Then we use the absorption-corrected light curves to test the various proposed models. SN 1980 k appears to be powered by a canonical shock, while SN 1979c is a good plerion candidate. An optical pulsar could still be detected at its location.

In this Paper, I consider physical processes, governing relativistic electrons in SNRs.

1. a) SNRs at the age t > 102 yr. I argue that the shock wave acceleration faces some difficulties. Then I show that the temporal evolution of the SNRs radio emission can be accounted for without involving the acceleration.

2. b) SNRs at the age t < 102 yr. I associate the lack of radio emission at this stage (Brown and Marscher, 1978) with the weakness of the magnetic field.

3. c) I infer that the most efficient particle acceleration and radio emission of the SNRs should occur at the stage t ~ 102 yr.

The acceleration of relativistic electrons by hydromagnetic turbulence in shell-type supernova remnants (SNRs) is examined within the framework of previous studies of their structural evolution through interaction with the interstellar medium. The predicted evolution of the synchrotron radio emission by the electrons is in agreement with a wide variety of observations.

Over the past decade there has been an increasing tempo of detailed optical and UV spectroscopy of SNR leading to comparisons with prevailing models of radiative shocks.

We review results obtained with the Focal Plane Crystal Spectrometer (FPCS) on the Einstein Observatory. Clear evidence is found for departures from ionization equilibrium in the interior of Puppis A. This comes from the observed weakness of the forbidden lines relative to the resonance lines for the He - like triplets of O VII and Ne IX. However, it is shown that this departure from equilibrium does not alter our conclusion, based on previous FPCS results, that O and Ne are overabundant relative to Fe. The spectrum of N132D shows strong O VIII emission and very weak Fe emission, suggesting an even greater O/Fe abundance enhancement than in Puppis A. In the Cygnus Loop, the O to Ne abundance ratio is approximately solar; we have no information about Fe. The O VII triplet shows clear evidence for departures from ionization equilibrium in the Cygnus Loop. The spectrum of Tycho's SNR contains lines from ionization stages of Fe XVII through Fe XXIII and XXIV, indicating that a wide range of ionization conditions are present. Cas A and Kepler's SNR show relatively less emission from the higher ionization stages. For Tycho, we measured the strength of the strong Si XIII lines, and we find that a many-fold overabundance of Si relative to Fe is required regardless of the equilibrium state of the emitting plasma (confirming the Solid State Spectrometer results). On a separate topic, the completed analysis of X-ray Doppler shifts in Cas A suggests that the emitting material is concentrated in a ring that is inclined to the line of sight and is expanding at ~5000 km s−1.

SNR can generally be recognized as extended sources of continuum radio emission with non-thermal spectra located near the galactic plane. The emission is synchrotron radiation from relativistic electrons which have either been accelerated or trapped in the expanding shell and its associated shocks. Early lists of remnants (e.g. Milne 1970) were culled from general catalogs of radio sources and confirmed by several other kinds of evidence including the presence of shell structure, significant polarization, lack of recombination line emission, strong optical [S II] lines, and soft x-ray emission. While a few efforts to detect more data on faint remnants are continuing (e.g. Bonsignori and Tomasi 1979; Reich and Braunsfurth 1981), about 150 SNR are now known in the Milky Way and most studies have turned to detailed investigation of specific objects to determine their energy sources, emission mechanisms, and interactions with their surroundings. These studies have shown that while most remnants fall within two general categories, standard shell and filled center, there is no unique evolution within a class and irregularities in the local interstellar medium dominate any statistical properties of individual remnants. A few objects, in particular Cas A and CTB80, do not fit within either category.

Our understanding of the structure of radiative shocks of modest (vs ≲ 200 km s−1) velocity has improved greatly since the pioneering work of Cox (1972). This advance has been accomplished primarily by a more complete development of the physics of the shock front, its ionisation precursor and of the cool recombination zone. (Dopita 1976, 1977; Raymond 1979; Shull and McKee 1979; Shull, Seab and McKee, this conference; D'Odorico and Dopita, this conference). However, all models used for spectrum synthesis have so far involved one dimensional steadyflow hydrodynamics and most have covered only a very limited range in parameter space. This has meant that whilst they can be used to estimate shock velocities and metallicities of the (assumed) fully radiative shocks found in nearby SNRs, they are of limited applicability in more exotic types of objects.

Faint filaments are observed a few arcmin outside the bright optical filaments of the Cygnus Loop. They show nearly pure Balmer line emission spectra, and they are interpreted as emission from non-radiative shocks (1). Each neutral H atom passing through the shock front emits on average about 0.1 Hα photon before it is ionized. Since this radiation arises very close to the shock front, rather than in an extended post-shock cooling zone (2), it can be used to study the physics of the shock front itself. The structure of a shock poses several important questions (3). There may be an electron thermal conduction precursor ahead of the shock and there may be plasma turbulence. The shock thermalizes 3/4 of the bulk velocity of the incoming particles, so the ions initially have nearly all of the thermal energy. The electron and ion temperatures can reach equilibrium on the Coulomb collision time scale, but plasma turbulence may bring them into equilibrium much more rapidly. The Coulomb equilibration time scale is similar to the hydrogen ionization time, so that the hydrogen line emission will depend on the nature of the equilibration. The interpretation of the Hα line profile in terms of the shock velocity also depends on this equilibration, so this question is important for comparison of shock models with X-ray spectra.

The spectral range redwards of about 7300 Angströms has up to now been rarely explored for any kind of object because of lack of adequate detectors. This situation is changing with the availability of silicon detectors whose response extends up to 1.1μ with reasonable quantum efficiency. We have used the ESO Reticon System behind the Boller and Chivens Spectrograph at the Cassegrain focus of the ESO 3.6m telescope to obtain spectra of several Supernova Remnants in the range 6000–10500 Å. The spectral resolution was 8 å and the dual array allowed a clear sky-subtraction, indispensable because of the presence of numerous atmospheric OH bands in this region. Data reduction was done with standard techniques using wavelength calibration, flat-field correction, response curve determination through observations of standard stars and extinction correction. We present below results based on the first spectra obtained for the Galactic remnants RCW 86, RCW 103 and Kepler SNR and the Magellanic Cloud ones N 49 and N 63A. The Crab Nebula will be discussed separately at the end.

Spectra for five different positions in RCW103 were obtained with the 1.5m and 4m telescopes of CTIO equiped with a SIT Vidicon detector.

From the observed Hα/Hβ ratio we found a variation of about 1.5 magnitudes in reddening for different filaments. The minimum value of Av found was 4.4 magnitudes implying a distance of 6.5 kpc.

Temperatures of about 105 K and densities of 70 cm−3 were found. Nitrogen is overabundant at least by a factor 3.

High resolution X-ray spectroscopy of the brightest knot of emission in the Puppis A supernova remnant shows that it is made up of ionizing plasma, far from equilibrium. Flux measurements in several X-ray lines enable us to determine the non-equilibrium conditions: electron temperature, ion populations, and time since the knot was heated by the supernova shock. Imaging and spectroscopic data from the Einstein Observatory together suggest that this knot is a cloud of density about 10 cm−3 which has recently been shocked to a temperature 7 × 106 K. Radio and optical data on the region appear consistent with this picture.

High quality X-ray spectral and imaging observations of the Cygnus Loop have been obtained with three different instruments. The High Resolution Imager (HRI) on the Einstein Observatory was used to obtain arcsecond resolution images of select bright regions in the Cygnus Loop which permit detailed comparisons between the X-ray, optical, and radio structure of the Loop. The Imaging Proportional Counter (IPC) on the Einstein Observatory was used to obtain an arcminute resolution map of essentially the full Loop structure. Finally, an Imaging Gas Scintillation Proportional Counter (IGSPC), carried aloft by a sounding rocket last fall, obtained modest resolution, spatially resolved spectrophotometry of the Cygnus Loop. An X-ray map of the Loop in the energy of the 0 VIII line was obtained. These data combine to yield a very powerful probe of the abundance, temperature, and density distribution of material in the supernova remnant, and in the interstellar medium.

In this paper we present a theoretical model of the Cygnus Loop which, with only a small number of free parameters, accounts for most of the gross features of the observations. We believe that none of the models described in the literature can explain the observations in such a simple way.