Re-identification of G35.6-0.4 as a supernova remnant

G35.6-0.4 is an extended radio source in the Galactic plane which has previously been identified as either a supernova remnant or an HII region. Observations from the Very Large Array Galactic Plane Survey at 1.4 GHz with a resolution of 1 arcmin allow the extent of G35.6-0.4 to be defined for the first time. Comparison with other radio survey observations show that this source has a non-thermal spectral index, with S ~ ν^-0.47+/-0.07. G35.6-0.4 does not have obvious associated infrared emission, so it is identified as a Galactic supernova remnant, not an HII region. It is ~15 × 11arcmin² in extent, showing partial limb brightening.