SIMBAD references

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 (V2487Oph). The recently discovered nova, V2491Cyg, is one of the fastest (He/N) novae observed to date. Using archival ROSAT, XMM-Newton, and Swift data, we show that V2491Cyg 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.