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

Abstract

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 A and [O II] 3727 A 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 � ‐D relation (4 kpc) are in good agreement.