Title:[0594] Cassiopeia A: radio image Caption:Cas A is the brightest nonsolar radio source in the sky. Its radio emission is synchrotron radiation produced by electrons moving in a magnetic field. This slide shows a fully processed radiograph obtained at the VLA of the total intensity of Cassiopeia A, at a wavelength of 6 cm. This image spans 6.1 x 6.1 arc minutes with 0.4-arc second resolution. Cassiopeia A is the remnant of the supernova event which was quite possibly that witnessed by Flamsteed in August 1680. At that time the outer layers of a massive star were ejected with high velocity, sweeping up a shell of the surrounding interstellar material. The fainter outer radio shell is believed to correspond to this swept-up gas. This shell has now decelerated sufficiently that the expanding material from deeper within the star is breaking through the shell from inside. The brighter inner shell is ejecta from the star and corresponds to the same regions in which fast-moving (6000 km/sec) optical knots have been found. The passage of this ejecta through the outer shell gives rise to conical extensions, which leave crater-like structures in their wake. Individual bright knots appear or fade on a time scale of a few years. The overall radio brightness of Cas A is declining by about 1 to 2 percent every year. Copyright:(c) Smithsonian Astrophysical Observatory Credit:Courtesy of NRAO/AUI

Title:[0595] Cassiopeia A: X-ray image Caption:Einstein x-ray images and spectra have demonstrated that much can be learned from x-ray observations of supernova remnants. This figure shows an x-ray image of the supernova remnant Cas A which exploded about 300 years ago. The x-ray emission is due to radiation from very hot gas (5 x 107 K).The bright clumpy shell of emission has a diameter of approximately 3 1/2 arc minutes. As also seen in the radio image, a second fainter shell surrounds the bright, inner shell. The outer shell may be due to emission from the shocked interstellar medium, while the inner shell is gas ejected by the supernova . About 15 solar masses of material are observed in the inner shell. Copyright:(c) Smithsonian Astrophysical Observatory Credit:Smithsonian Institution Astrophysical Observatory

Title:[0554] All-sky survey: radio map Caption:The 408 MHz (73-cm wavelength) all-sky survey is shown in false color in galactic coordinates. The radio intensities are displayed in a linear color scale going from deep blue (lowest intensities) to red (highest intensities). The angular resolution of the map is ~2 degrees. A number of well-known sources are seen along the galactic plane including the Cas A and Crab supernova remnants. The local arm complexes (Cygnus-X and Vela-X) stand out clearly surrounded by diffuse radio emission. The diffuse radio emission from the Milky Way is predominantly due to synchrotron radiation from cosmic-ray electrons interacting with magnetic fields in our galaxy. A large number of "spurs" can be seen above the galactic plane. The most prominent of these is the North Polar spur which may be the remnant of a nearby (500 light years distant), ancient (~300,000 years ago) supernova. In addition, numerous bright extragalactic objects can be recognized, e. g., Centaurus A, Virgo A, LMC and SMC. Our sister galaxy, M31, is seen as a light blue spot south of Cassiopeia A. Copyright:(c) Smithsonian Astrophysical Observatory Credit:Courtesy of CGT Haslam, CJ Salter, WE Wilson, and H Stoffel, Max Planck Institute fur Radioastronomie, Bonn