RADIO-EMISSION FROM THE SUPERNOVA REMNANT G160.9+2.6 (HB9)

We present new high-resolution observations of the 408 and 1420 MHz continuum emission from the large-angular-diameter supernova remnant G160.9 + 2.6 (HB9), and of the H I-line emission from the region of the remnant. The 1420 MHz images have a resolution (full-width, half power, EWxNS) of 1.0'x1.4', and are composites of synthesis observations of three separate fields and single-antenna observations of extended structure. The 408 MHz image is a similar composite with resolution 3.5'x4.8'. Emission from HB9 is dominated by filamentary arcs which extend across the face of the remnant. Where optical (H-alpha) filaments have been observed they generally correspond closely to the radio filaments. However, in at least three places we detect a slight outward displacement of the optical filament relative to its radio counterpart. One prominant radio filament in the northeast has no detectable optical filament despite an apparent lack of obscuration in this direction. Comparisons of the 408 and 1420 MHz images yield a mean spectral index (S-nu proportional nu-alpha) of alpha = 0.61 with an rms deviation of 0.08 on scale sizes of approximately 15% of the remnant's diameter. We find no correlation of the spectral index variations with type of structure, lending some support to the view that the diffuse and filamentary emissions differ only in the degree of alignment of the line of sight with tangencies to compressed sheets of emission. Our H I observations span the full range of Galactic radial velocity with a resolution of 1.3 km/s. No indication of any interaction of HB9 with the atomic component of surrounding gas is evident. A consideration of the H I emission, CO observations of molecular components associated with the H II regions Sh217 and Sh219, and the lack of extinction of optical filaments indicate that HB9 is at a distance less than 4 kpc. The mean radio brightness and x-ray flux lend support to the association of HB9 with the pulsar PSR0458 + 46, probably at a distance near 1.2 kpc.