G64.5+0.9: a new shell supernova remnant with unusual central emission

Abstract

We present observations between 1.4 and 18 GHz confirming that G64.5+0.9 is a new Galactic shell supernova remnant, using the Very Large Array and the Arcminute Microkelvin Imager. The remnant is a shell ≃8 arcmin in diameter with a spectral index of α= 0.47 ± 0.03 (with α defined such that flux density S varies with frequency ν as S∝ν−α). There is also emission near the centre of the shell, ≃1 arcmin in extent, with a spectral index of α= 0.81 ± 0.02. We do not find any evidence for spectral breaks for either source within our frequency range. The nature of the central object is unclear and requires further investigation, but we argue that it is most unlikely to be extragalactic. It is difficult to avoid the conclusion that it is associated with the shell, although its spectrum is very unlike that of known pulsar wind nebulae.