Multiwavelength study of a new Galactic SNR G332.5-5.6

We present compelling evidence for confirmation of a Galactic supernova remnant (SNR) candidate, G332.5-5.6, based initially on identification of new, filamentary, optical emission-line nebulosity seen in the arcsecond resolution images from the Anglo Australian Observatory (AAO)/United Kingdom Schmidt Telescope (UKST) Hα survey. The extant radio observations and X-ray data which we have independently re-reduced, together with new optical spectroscopy of the large-scale fragmented nebulosity, confirm the identification. Optical spectra, taken across five different, widely separated nebula regions of the remnant as seen in the Hα images, show average ratios of [N ii]/Hα = 2.42, [S ii]/Hα = 2.10 and [S ii] 6717/6731 = 1.23, as well as strong [O i] 6300, 6364 Å and [O ii] 3727 Å emission. These ratios are firmly 3within those typical of SNRs. Here, we also present the radio-continuum detection of the SNR at 20/13 cm from observations with the Australia Telescope Compact Array (ATCA). Radio emission is also seen at 4850 MHz, in the Parkes-MIT-NRAO (PMN) survey and at 843 MHz from the Sydney University Molonglo Sky Survey (SUMSS) survey. We estimate an angular diameter of ∼30 arcmin and obtain an average radio spectral index of α = -0.6 ± 0.1 which indicates the non-thermal nature of G332.5-5.6. Fresh analysis of existing ROSAT X-ray data in the vicinity also confirms the existence of the SNR. The distance to G332.5-5.6 has been independently estimated by Reynoso and Green as 3.4 kpc based on measurements of the H i λ21-cm line seen in absorption against the continuum emission. Our cruder estimates via assumptions on the height of the dust layer (3.1 kpc) and using the Σ-D relation (4 kpc) are in good agreement.