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


E-mail: (IN); (AS); (GK); (FH)


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 2009 July and revealed a double-peaked pulsation with a period of 743.38 ± 0.25 s. 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 results from a detailed analysis of the XMM–Newton observation, which also shows a double-peaked modulation, however shifted in phase, with a period of 742.35 ± 0.23 s. The X-ray spectra obtained from the XMM–Newton European Photon Imaging Camera (EPIC) instruments were modelled by a plasma emission and a soft blackbody component with a partial covering photoelectric absorption model with a 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 Fe xxvi lines (∼6.95 keV) are clearly resolved in the EPIC spectra. In the PorbPspin diagram of intermediate polars, V2069 Cyg shows a low spin-to-orbit ratio of ∼0.0276 in comparison with ∼0.1 for other intermediate polars.