Periodicities in the X-ray intensity variations of TV Columbae: an intermediate polar

Abstract

We present results from a temporal analysis of the longest and the most sensitive X-ray observations of TV Columbae- a cataclysmic variable classified as an intermediate polar. The observations were carried out with the Rossi X-Ray Timing Explorer (RXTE) Proportional Counter Array, ROSAT Position Sensitive Proportional Counter, and ASCA. Data were analyzed using a one-dimensional CLEAN and Bayesian algorithms. The presence of a nearly sinusoidal modulation due to the spin of the white dwarf is seen clearly in all the data, confirming the previous reports based on the EXOSAT data. An improved period of 1909.7±2.5 s is derived for the spin from the RXTE data. The binary period of 5.5 hr is detected unambiguously in X-rays for the first time. Several sidebands due to the interaction of these periods are observed in the power spectra, thereby suggesting contributions from both the disk-fed and the stream-fed accretion for TV Col. The accretion disk could perhaps be precessing, as sidebands due to the influence of 4 day period on the orbital period are seen. The presence of a significant power at certain sidebands of the spin frequency indicates that the emission poles are asymmetrically located. The strong power at the orbital sidebands seen in both the RXTE and ROSAT data gives an indication for an absorption site fixed in the orbital frame. Both the spin and the binary modulation are found to be energy dependent. The fact that the spin modulation amplitude in TV Col decreases with energy is confirmed. Hardness ratio variations and the energy-dependent modulation depth during the spin modulation can be explained by partially covered absorbers in the path of the X-ray emission region in the accretion stream. Increased hardness ratio during a broad dip in the intensity at binary phase of 0.75-1.0 confirms the presence of a strong attenuation due to additional absorbers, probably from an impact site of the accretion stream with the disk or magnetosphere.