Very fast photometric and X-ray observations of the intermediate polar V2069 Cygni (RX J2123.7+4217)

TL;DR

This study presents high-resolution optical and X-ray observations of the intermediate polar V2069 Cygni, revealing its white dwarf spin period, spectral features, and unique low spin-to-orbit ratio, advancing understanding of accretion processes.

Contribution

First simultaneous optical and X-ray timing analysis of V2069 Cygni, identifying its white dwarf spin period and detailed spectral characteristics with high temporal resolution.

Findings

Detected a 743.38 s optical spin period with double-peaked modulation.

X-ray analysis confirms a similar 742.35 s period, phase-shifted, with spectral modeling showing plasma and black body components.

V2069 Cygni exhibits an unusually low spin-to-orbit ratio of ~0.0276 among intermediate polars.

Abstract

We present fast timing photometric observations of the intermediate polar V2069 Cygni (RX J2123.7+4217) using the Optical Timing Analyzer (OPTIMA) at the 1.3 m telescope of Skinakas Observatory. The optical (450-950 nm) light curve of V2069 Cygni was measured with sub-second resolution for the first time during July 2009 and revealed a double-peaked pulsation with a period of 743.38 +0.25. A similar double-peaked modulation was found in the simultaneous Swift satellite observations. We suggest that this period represents the spin of the white dwarf accretor. Moreover, we present the results from a detailed analysis of the XMM-Newton observation that also shows a double-peaked modulation, however shifted in phase, with 742.35 +0.23 s period. The X-ray spectra obtained from the XMM-Newton EPIC (European Photon Imaging Camera) instruments were modelled by a plasma emission and a soft black body component with a partial covering photo-electric absorption model with covering fraction of 0.65. An additional Gaussian emission line at 6.385 keV with an equivalent width of 243 eV is required to account for fluorescent emission from neutral iron. The iron fluorescence (~6.4 keV) and FeXXVI lines (~6.95 keV) are clearly resolved in the EPIC spectra. In the Porb-Pspin diagram of IPs, V2069 Cyg shows a low spin to orbit ratio of ~0.0276 in comparison with ~0.1 for other intermediate polars.