The apparent synchronization of V1500 Cygni

We have used XMM-Newton and ground-based optical/near-infrared photometry to explore the old classical nova, and asynchronous polar V1500 Cyg. The X-ray light curve shows a single bright phase once per orbit, associated with the main accretion region. Analysis of the X-ray light curve indicates that the white dwarf spin period is now similar to the orbital period. When this inference is combined with the ground-based photometry, we find that the most probable explanation for the observed behaviour is a system that has become fully synchronized. The X-ray spectrum and luminosity of V1500 Cyg are consistent with a high state polar. The optical and near-IR light curves can partially be explained as a heavily irradiated secondary star, but exhibit strong deviations from that model. We find that the most likely explanation for the observed excesses in these light curves is cyclotron emission from distributed accretion regions, or from a multipole geometry.