Further Observations of the Peculiar Galactic Radio Source G318.9+0.4

Abstract

The core and arc systems of the peculiar Galactic supernova remnant G3 18.9+0.4 have been observed over the range 0.843 to 8.55 GHz. A new image at 0.843 GHz shows evidence for at least one new arc in the object. Total intensity and polarization observations at 4.5 and 8.55 GHz are also presented. These imply an overall spectral index of α<SUP>8.55</SUP><SUB>0.843</SUB> = -.2±0.1, and give polarizations of ∼5% and 20% at 4.5 and 8.55 GHz, respectively. High-resolution observations made with the Australia Telescope Compact Array at 1.4 and 4.8 GHz show the detailed structure of the core and adjacent arcs, revealing a remarkable complex of ridges and filaments in the core component and the presence of a jetlike feature extending radially from the core to the nearby arc structure. While no satisfactory theory is yet available to explain the irregular brightness distribution of G3 18.9+0.4, the new observations show that the structure of the core component bears a close resemblance to certain features in CTB 80, prompting speculation that a similar excitation mechanism occurs in both objects.