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

¹ Dept. of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UK e-mail: kpa@star.le.ac.uk
² XMM-Newton Science Operations Centre, ESAC, Apartado 78, 28691 Villanueva de la Cañada, Madrid, Spain
³ Astrophysics Research Institute, Liverpool John Moores University, Birkenhead, CH41 1LD, UK
⁴ Department of Geology and Astronomy, West Chester University, West Chester, PA 19383, USA
⁵ School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404, USA

Received: 24 July 2009
Accepted: 8 September 2009

Abstract

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 –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  eV and place a limit on the density of the surrounding medium of log (n_e/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 Å) between days 169 and 255.