Timing and Spectral Studies of the Transient X-Ray Pulsar EXO 053109–6609.2 with ASCA and BeppoSAX

We report timing and spectral properties of the transient Be X-ray pulsar EXO 053109-6609.2, which was studied using observations made with the ASCA and BeppoSAX observatories. Although there must have been at least one spin-down episode of the pulsar since its discovery, the new pulse-period measurements show a monotonic spin-up trend since 1996. The pulse profile is found to have marginal energy dependence. There is also evidence for strong luminosity dependence of the pulse profile, which has a single-peaked profile at low luminosity that changes to a double-peaked profile at high luminosity. This suggests a change in the accretion pattern at certain luminosity levels. The X-ray spectrum is found to consist of a simple power law with a photon index in the range of 0.4-0.8. At high intensity levels the spectrum also shows the presence of a weak iron emission line.