X-ray and UV observations of nova V598 Puppis between 147 and 255 days after outburst

Aims. The launch of Swift has allowed many more novae to be observed regularly over the X-ray band. Such X-ray observations of novae can reveal ejecta shocks and the nuclear burning white dwarf, allowing estimates to be made of the ejecta velocity. Methods. We analyse XMM-Newton and Swift X-ray and UV observations of the nova V598 Pup, which was initially discovered in the XMM-Newton slew survey. These data were obtained between 147 and 255 days after the nova outburst, and are compared with the earlier, brighter slew detection. Results. The X-ray spectrum consists of a super-soft source, with the soft emission becoming hotter and much fainter between days ∼147 and ∼172 after the outburst, and a more slowly declining optically thin component, formed by shocks with kT ∼ 200–800 eV (corresponding to velocities of 400–800 km s −1 ). The main super-soft phase had a duration of less than 130 days. The Reflection Grating Spectrometer data show evidence of emission lines consistent with optically thin emission of kT ∼ 100 eV and place a limit on the density of the surrounding medium of log (ne/cm −3 ) < 10.4 at the 90% level. The UV emission is variable over short timescales and fades by at least one magnitude (at λ ∼ 2246–2600 A) between days 169 and 255.