New observations at 232 MHz have been combined with a re-analysis of several other existing sets of data to obtain the spectrum of the unusual supernova remnant G76.9+1.0 below 5 GHz. In order to demonstrate the reliability of the 232-MHz observations and to calibrate them, the spectra of fifteen other radio sources in the area of G76.9+1.0 have also been derived. With one possible exception, the 232-MHz flux densities agree well with those expected from the spectra and characters of these sources. The principal result to emerge from this study is that the spectrum of G76.9+1.0, which is a filled-centre SNR, appears to flatten below 1 GHz. Such a spectral break has been found or suspected in other filled-centre remnants. Further low-frequency observations of G76.9+1.0 will be required, however, before such a break can be firmly established.
This study has also contributed new low-frequency information on the integrated spectra of the other sources in the area surrounding G76.9+1.0. These include several HII regions, another filled-centre SNR, and several extragalactic sources. Two steep-spectrum sources probably warrant further investigation. Crude ``representative'' physical models have been fitted approximately to the HII region spectra. The most significant conclusion is that very clumpy models are required, consisting of ``knots'' of emission measure with low filling factors.
Acknowledgements
We are grateful to Dr. S. Pineault for providing unpublished 408-MHz data, and to Drs. A.R. Taylor and B.J. Wallace for providing the 327-MHz data. We thank the referee, E. Fürst, for several suggestions for improvements in the paper. This work was carried out under the China-Canada Scientific Exchange agreement, which operates under the auspices of the Chinese Academy of Sciences and the National Research Council of Canada. Zhang Xi-zhen and Zheng Yi-jia are grateful to DRAO for hospitality during their stay in Canada. DRAO is operated as a national facility by the National Research Council of Canada.