X-ray variability and 1mHz oscillations in TT Arietis.

Using the archival ROSAT observation of TT Ari, X-ray energy spectra in different orbital phases and power spectra of the intensity time series are presented. Spectral fits show that the source gets brighter during the observation. The orbital modulation of the X-ray counting rate and bremsstrahlung temperature suggests that soft X-ray emission peaks in the orbital phase interval 0.75-0.90, when an outer disk hot spot is near the line of sight. This correlates with the orbital modulation of C IV(λ1549) absorption (Robinson & Cordova 1993). Timing analysis indicates that while the source gets brighter, the frequency of the 1mHz oscillation is not correlated with X-ray intensity. This implies that in the X-rays from TT Ari, the beat frequency model is not appropriate for explaining the changes in the 1mHz oscillations.