On the Long-Term Light Curve Behaviour of the Intermediate Polar TX Col

Abstract

TX Col (1H0547–407; Porb = 5.72 h) is an intermediate polar (IP) with spin and synodic (beat) periods of 1911s and 2106 s respectively (Buckley & Tuohy 1989). EXOSAT observations (Tuohy et al. 1986) showed the beat period dominated at higher energies (ME; 1… 9keV), while the spin period was stronger in softer X-rays (LE1; 0.1… IkeV). The high flux level, and pulse fraction (>70%), of the soft X-rays were unique in an IP at that time. Now three other IPs, recently discovered from the ROSAT survey, have been found to show a true separate soft X-ray component, similar to the polars (Motch & Haberl 1994).The strength of the synodic X-ray period in TX Col was, until the recent discovery of the variable polarised IP, RX J1712.6–2414 (Buckley et al. 1995), unique. This was taken as evidence for direct accretion onto the magnetosphere (e.g. Mason, Rosen & Hellier 1988), through a component of the accretion stream overflowing the disc (Hellier 1992).