Letter to the Editor

Pre-nova X-ray observations of V2491 Cygni (Nova Cyg 2008b)

¹ ESA, European Space Astronomy Centre (ESAC), Apartado 78, 28691 Villanueva de la Cañada (Madrid), Spain e-mail: Aitor.Ibarra@sciops.esa.int
² The Department of Physics and Astronomy, The University of Leicester, Leicester, LE1 7RH, UK
³ NASA/Goddard Space Flight Center, Code 662, Greenbelt, MD 20771, USA
⁴ University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA
⁵ ISDC Data Centre for Astrophysics, Chemin d'Écogia 16, 1290 Versoix, Switzerland
⁶ Observatoire Astronimique de l'Université de Genève, Chemin des Maillettes 51, 1290 Sauverny, Switzerland
⁷ Astroph. Research Institute, Liverpool John Moores Univ., Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD 7, UK
⁸ IEEC-CSIC, Campus UAB, Facultat Ciències, C5-par, 2on, 08193 Bellaterra, Spain
⁹ CRESST and X-ray Astrophysics Laboratory NASA/GSFC, Greenbelt, MD 20771, USA
¹⁰ INAF – Osservatorio Astronomico di Padova, vicolo Osservatorio 5, 35122 Padova, Italy
¹¹ Department of Astronomy, University of Wisconsin, 475 N. Charter Str., Madison WI 53706, USA
¹² Grup d'Astronomia i Astrofísica, Dept. Física i Enginyeria Nuclear, Univ. Politècnica de Catalunya, 08036 Barcelona, Spain
¹³ School of Earth & Space Exploration, Arizona State University, PO Box 871404, AZ 85287-1404, USA

Received: 23 January 2009
Accepted: 23 February 2009

Abstract

Classical novae are phenomena caused by explosive hydrogen burning onto an accreting white dwarf. Only one classical nova had been identified in X-rays before the actual optical outburst occurred (V2487 Oph). The recently discovered nova, V2491 Cyg, is one of the fastest (He/N) novae observed to date. Using archival ROSAT, XMM-Newton, and Swift data, we show that V2491 Cyg was a persistent X-ray source during its quiescent time before the optical outburst. We present the X-ray spectral characteristics and derive X-ray fluxes. The pre-outburst X-ray emission is variable, and, at least in one observation, it exhibits a soft X-ray source.