Timing and spectral studies of the transient X-ray pulsar EXO   053109-6609.2 with ASCA and Beppo-SAX
  We report timing and spectral properties of the transient Be X-ray pulsar EXO 053109--6609.2 studied using observations made with the ASCA and BeppoSAX observatories. Though 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, 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 level. The X-ray spectrum is found to consist of a simple power-law with photon index in the range of 0.4--0.8. At high intensity level the spectrum also shows presence of weak iron emission line. 
B. Paul (1), S. N. A. Jaaffery (2), S. Naik (1,3) and P. C. Agrawal   (1) ((1) Department of Astronomy and Astrophysics, Tat...