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

TL;DR

This paper reports on the pre-nova X-ray activity of V2491 Cyg, revealing it was a persistent and variable X-ray source before its optical outburst, with spectral analysis indicating soft X-ray emission at times.

Contribution

It provides the first detailed analysis of pre-outburst X-ray observations of V2491 Cyg, using archival data to characterize its X-ray variability and spectral properties.

Findings

V2491 Cyg was a persistent X-ray source before outburst

Pre-outburst X-ray emission showed variability

Detected very soft X-ray emission in at least one observation

Abstract

Classical novae are phenomena caused by explosive hydrogen burning on an accreting white dwarf. So far, only one classical nova has 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 so far. 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 shows a very soft X-ray source.