The unusual supernova remnant G76.9+1.0: The low-frequency radio spectrum

¹ Dominion Radio Astrophysical Observatory, National Research Council, Box 248, Penticton, British Columbia V2A 6K3, Canada
² Beijing Astronomical Observatory, Chinese Academy of Sciences, Beijing 100080, China

Send offprint request to: T.L. Landecker

Received: 19 January 1996
Accepted: 11 September 1996

Abstract

G76.9+1.0 is an unusual radio source which is interpreted as a filled-centre supernova remnant (SNR). New 232-MHz observations of a field containing G76.9+1.0 have been combined with a re-analysis of existing observational data to derive the low-frequency spectrum of the SNR. Its spectral index has a value of about 0.6 above 1 GHz, and appears to flatten below that frequency. This may indicate a “break” in the spectrum below 1 GHz. However, further observations at frequencies below 400 MHz will be required before this can be firmly established. The low-frequency spectra of several other radio sources in the field surrounding G76.9+1.0 were also derived, partially to confirm the validity of the 232-MHz flux densities but also to provide new lower frequency data for these objects. They include several H ii regions and some extragalactic sources. Two of the latter have rather steep spectra and merit further study.