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Classical novae are phenomena caused by explosive hydrogen burning on anaccreting white dwarf. So far, only one classical nova has been identified inX-rays before the actual optical outburst occurred (V2487 Oph). The recentlydiscovered nova, V2491 Cyg, is one of the fastest (He/N) novae observed so far.Using archival ROSAT, XMM-Newton and Swift data, we show that V2491 Cyg was apersistent X-ray source during its quiescent time before the optical outburst.We present the X-ray spectral characteristics and derive X-ray fluxes. Thepre-outburst X-ray emission is variable, and at least in one observation itshows a very soft X-ray source.

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