G 32.1 — 0.9: a new Galactic supernova remnant?

• Published in: Monthly notices of the Royal Astronomical Society 1997-12, Vol.292 (2), p.365-377
• Main Authors: Folgheraiter, E. L., Warwick, R. S., Watson, M. G., Koyama, K.
• Format: Article
• Language: English
• Subjects: ISM: individual: G 32.1 — 0.9; supernova remnants; X-rays: ISM
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/292.2.365

A low surface brightness X-ray source detected serendipitously in ROSAT observations of the Galactic plane near l≈ 32° is probably a previously unknown Galactic supernova remnant (SNR). The source, designated G 32.1—0.9, has an approximate angular size of 30 × 30 arcmin2 and an irregular X-ray morphology with brightening towards the centre. The X-ray spectrum measured by both ROSAT and ASCA is well characterized by a thermal model with a temperature ∼0.8 keV and a subsolar metallicity (∼0.2). The measured soft X-ray absorption is equivalent to a column density NH∼ 2.3 × 1021 cm ∼2, which is about one-quarter of the full Galactic NH in this direction, thus implying a Galactic origin for the source. The enhanced radio emission in the region of G 32.1 — 0.9 is plausibly interpreted as a low surface brightness partial radio shell. On the basis of the X-ray morphology and X-ray spectrum, coupled with the (albeit less secure) radio evidence, we conclude that G 32.1 — 0.9 is probably a new composite-type Galactic SNR. There are three bright X-ray hotspots, one in each of the north-eastern, south-eastern and south-western quadrants of the source. The first (referred to as hotspot A) has a considerably harder spectrum than the rest of the object and could be an embedded source within the putative SNR or a more distant interloper in chance positional coincidence with G 32.1 — 0.9. All three hotspots could represent regions where the supernova blast-wave has encountered regions of enhanced density within the local ISM. A Sedov analysis gives the distance of G 32.1—0.9 to be ∼4.6 kpc. The age of the remnant is then ∼ 12 000 yr, and the derived luminosity is Lx∼8 × 1034 erg s−1.