Confirmation of G6.31+0.54 as a part of a Galactic supernova remnant
  A combination of archival multi-frequency radio observations with narrow-band
HAlpha optical imagery and new confirmatory optical spectroscopy have shown
that candidate supernova remnant G6.31+0.54 can now be confirmed as part of a
Galactic supernova remnant (SNR). It has non-thermal emission, an optical
emission line spectrum displaying shock excitation and standard SNR line
ratios, fine filamentary structures in HAlpha typical of optical remnants and
closely overlapping radio and optical footprints. An X-ray ROSAT source 1RXS
J175752.1-231105 was also found that matches the radio and optical emission
though a definite association is not proven. Nevertheless, taken together, all
these observed properties point to a clear SNR identification for this source.
We provide a rough estimate for the kinematic distance to G6.31+0.54 of
~4.5kpc. The detected optical filaments are some ~10arcminutes in extent (or
about 13 pc at the assumed distance). However, as only a partial arcuate
structure of the SNR can be seen (and not a full shell) the full angular extent
of the SNR is unclear. Hence the physical extent of the observed partial shell
is also difficult to estimate. If we assume an approximately circular shell
then a conservative fit to the optical arc shaped filaments gives an angular
diameter of ~20 arcminutes corresponding to a physical diameter of ~26 pc that
shows this to be an evolved remnant.
