Suzaku observation of the classical nova V2491 Cyg in quiescence

TL;DR

This study reports Suzaku X-ray observations of the nova V2491 Cyg in quiescence, revealing a luminous, multi-component spectrum with potential signs of localized hydrogen burning or accretion onto a magnetic white dwarf, suggesting it may be a soft intermediate polar.

Contribution

First detailed Suzaku X-ray analysis of V2491 Cyg in quiescence, proposing its classification as a potential soft intermediate polar based on spectral and timing features.

Findings

Detection of a soft blackbody component at 0.5 keV

X-ray modulation with a 38-minute period

Spectral fit includes thermal plasma, blackbody, and complex absorber

Abstract

We present Suzaku XIS observation of V2491 Cyg (Nova Cyg 2008 No. 2) obtained in quiescence, more than two years after the outburst. The nova was detected as a very luminous source in a wide spectral range from soft to hard X-rays. A very soft blackbody-like component peaking at 0.5 keV indicates that either we observe remaining, localized hydrogen burning on the surface of the white dwarf, or accretion onto a magnetized polar cap. In the second case, V2491 Cyg is a candidate "soft intermediate polar". We obtained the best fit for the X-ray spectra with several components: two of thermal plasma, a blackbody and a complex absorber. The later is typical of intermediate polars. The X-ray light-curve shows a modulation with a $\sim$38 min period. The amplitude of this modulation is strongly energy dependent and reaches maximum in the 0.8--2.0 keV range. We discuss the origin of the X-ray emission and pulsations, and the likelihood of the intermediate polar scenario.