X-ray and radio observations of the γ Cygni supernova remnant G78.2+2.1

We analyse ROSAT and Chandra Advanced CCD Imaging Spectrometer (ACIS) X-ray observations and H i absorption spectra of the gamma Cygni supernova remnant (G78.2+2.1, DR4). The ROSAT All-Sky Survey image shows that G78.2+2.1 has an adjacent limb-brightened shell north of it. A new ROSAT mosaic shows details of the X-ray emission over the entire face of G78.2+2.1. We also create Chandra mosaics that cover much of the northern rim and central regions of G78.2+2.1. The H i absorption spectra result in the association of G78.2+2.1 with the gamma Cygni nebula, with a distance of 1.7-2.6 kpc. The Chandra spectra for G78.2+2.1 give an X-ray temperature of 0.6-1.2 keV (90 per cent error), and they show that a Sedov model has an age of 6800-10 000 yr. A compact power-law X-ray source in G78.2+2.1 is consistent with the same distance as G78.2+2.1. The northern X-ray shell is identified with a B3 star at a distance of 980 pc and it is proposed that this is a stellar wind bubble.