The Supernova Remnant Cassiopeia A at Millimeter Wavelengths

We used the BIMA array to map the supernova remnant Cas A from 28 to 87 GHz with 2'' to 7'' angular resolution. Data from 75 to 87 GHz with 19 pointing centers were combined with single-dish data to form a completely sampled image. These new BIMA images were compared with VLA images at 1.5 and 5 GHz to look for spectral index variations across Cas A. The images were spatially filtered and convolved to a common sampled UV range corresponding to angular scales from 7'' to 95''. The images give direct evidence for a steeper spectral index in the knots outside the bright ring. Analysis of the 26 brightest peaks gives statistical evidence for spectral index variations throughout the remnant. The high-frequency spectra confirm and extend the spectral variations seen previously at lower frequencies. The spectra are largely consistent with different power laws and not curved spectra. This provides strong support for local variations in the acceleration of relativistic particles in Cas A.

[1]  J. Keohane,et al.  The X-Ray Expansion of the Supernova Remnant Cassiopeia A , 1998, astro-ph/9806241.

[2]  L. Rudnick,et al.  An Analysis of the Synchrotron Spectrum in the Fanaroff-Riley Type I Galaxy 3C 449 , 1997 .

[3]  G. E. Allen,et al.  Evidence of X-Ray Synchrotron Emission from Electrons Accelerated to 40 TeV in the Supernova Remnant Cassiopeia A , 1997, astro-ph/9707110.

[4]  R. Sault,et al.  An approach to interferometric mosaicing , 1996 .

[5]  J. Blondin,et al.  A Circumstellar Shell Model for the Cassiopeia A Supernova Remnant , 1996 .

[6]  M. Norman,et al.  Interaction of Rayleigh-Taylor Fingers and Circumstellar Cloudlets in Young Supernova Remnants , 1996, astro-ph/9606093.

[7]  Lee G. Mundy,et al.  The Berkeley-Illinois-Maryland-association millimeter array , 1996 .

[8]  Lawrence Rudnick,et al.  Sites of Relativistic Particle Acceleration in Supernova Remnant Cassiopeia A , 1996 .

[9]  Namir E. Kassim,et al.  Evidence for Thermal Absorption inside Cassiopeia A , 1995 .

[10]  A. Fabian,et al.  The Three-dimensional Structure of the Cassiopeia A Supernova Remnant. I. The Spherical Shell , 1995 .

[11]  T. Jones,et al.  The dynamical and radiative evolution of clumpy supernova ejecta , 1994 .

[12]  E. M. Jones,et al.  Radio emission from young supernova remnants. II: Evolution and dependence on characteristics of the progenitor and the external medium , 1993 .

[13]  L. Rudnick,et al.  Determining the shape of spectra in extended radio sources , 1993 .

[14]  M. Wright,et al.  Mapping Cygnus A at 3 millimeter wavelength with the MIRIAD system , 1993 .

[15]  S. Reynolds,et al.  Electron acceleration in Tycho's and Kepler's supernova remnants - Spectral evidence of Fermi shock acceleration , 1992 .

[16]  D. A. Green,et al.  Upper limits on the infrared flux density of the ‘filled-centre’ supernova remnant 3C58 , 1992 .

[17]  T. Jones,et al.  Cosmic-ray-modified supernova remnant shocks , 1992 .

[18]  Richard A. Perley,et al.  Relativistic Electron Populations in Cassiopeia A , 1991 .

[19]  T. Jones,et al.  Numerical studies of diffusive particle acceleration in supernova remnants , 1990 .

[20]  R. Chevalier,et al.  The interaction of supernovae with circumstellar bubbles , 1989 .

[21]  H. Voelk,et al.  Maximum energy of cosmic-ray particles accelerated by supernova remnant shocks in stellar wind cavities , 1988 .

[22]  Richard A. Perley,et al.  Physical process which shapes Cassiopeia A , 1987, Nature.

[23]  R. Arendt,et al.  Resolution of compact knots in Cassiopeia A , 1987 .

[24]  J. Borovsky,et al.  A study of the stochastic energization of charged particles with and without synchrotron energy loss , 1986 .

[25]  J. Kenney,et al.  Cassiopeia A at 86 Gigahertz : spectral and rotation measure differences. , 1985 .

[26]  W. Ashworth.  A Probable Flamsteed Observation of the Cassiopeia a Supernova , 1979 .

[27]  Jeremiah P. Ostriker,et al.  Particle Acceleration by Astrophysical Shocks , 1978 .

[28]  E. Olsen,et al.  The evolution of the radio spectrum of Cassiopeia A , 1974 .