Pre-nova X-ray observations of V2491 Cygni (Nova Cyg 2008b)
Mukai, K.; Hernanz, M.; Sala, G.; Orio, M.; Osborne, J. P.; Starrfield, S.; Kuulkers, E.; Bode, M. F.; Saxton, R. D.; Wynn, G. A.; Beckmann, V.; Page, K.; Ness, J. U.; Baumgartner, W.; Ibarra, A.
Spain, United Kingdom, United States, Switzerland, Italy
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.