G65.2+5.7: A Thermal Composite Supernova Remnant with a Cool Shell

This paper presents archival ROSAT PSPC observations of the G65.2+5.7supernova remnant (also known as G65.3+5.7). Little material obscures thisremnant and so it was well observed, even at the softest end of ROSAT'sbandpass (~0.11 to 0.28 keV). These soft X-ray images reveal the remnant'scentrally-filled morphology which, in combination with existing radio frequencyobservations, places G65.2+5.7 in the thermal composite (mixed morphology)class of supernova remnants. Not only might G65.2+5.7 be the oldest knownthermal composite supernova remnant, but owing to its optically revealed cool,dense shell, this remnant supports the proposal that thermal compositesupernova remnants lack X-ray bright shells because they have evolved beyondthe adiabatic phase. These observations also reveal a slightly extended pointsource centered on RA = 19h 36m 46s, dec = 30deg 40' 07'' and extending 6.5arcmin in radius in the band 67 map. The source of this emission has yet to bediscovered, as there is no known pulsar at this location.Comment: In AASTEX preprint form, document is 12 pages long and includes 3 figure file