MULTIFREQUENCY RADIO SPECTRAL STUDIES OF THE SUPERNOVA REMNANT G78.2+2.1

A new map of the SNR G78.2+2.1 at 232 MHz is presented. This map is us ed with other images at 408, 1420, 2695 and 4800 MHz to investigate th e total spectral index of the SNR and the variation of spectral index across it. The integrated spectral index is alpha = 0.54 +/- 0.02 (whe re S-nu proportional to nu(-alpha)). Maps of the spectral-index variat ion across the source are derived using a method which calculates a di fferential spectral index. This method is independent of offset errors and large-scale background variations. Systematic spectral-index vari ations of similar to +/- 0.15 are found, consistently in the many inde pendent pairs of data sets. Regions of higher spectral index (steeper spectra) appear around the periphery of the remnant and in its central area. Regions of lower spectral index (flatter spectra) are also foun d within the remnant. The latter may result from a change in the natur e of the non-thermal emission or may represent ''contamination'' from underlying patches of thermal emission. There is no clear correlation of spectral index with intensity across the SNR. Theoretical reasons f or spectral-index variations have been explored but no clear interpret ation of the apparent spectral steepening near the shock front has bee n found nor has an explanation of the steep-spectrum central region.