Temporal analysis of EXO 0531-66 in outburst

Abstract

We report a timing analysis of the Be transient X-ray binary EXO 053109-6609.2 in outburst observed with BeppoSAX. The luminosity of the source is similar to 1.1 x 10(37) ergs s(-1), similar to that observed in the previous three outbursts. The source shows pulsations from 0.1 up to 60 keV. The pulsed fraction does not seem to decrease with the energy. The pulse profile is double peaked in the whole energy band. The barycentric pulse period is 13.67590 +/- 0.00008 s at MJD 50,520.0. The average rate of period change during the similar to 2 days of BeppoSAX observation is (3.7 +/- 0.5) x 10(-9) s s(-1). Comparison with ROSAT data allowed the determination of a secular spin-down (P) over dot (sec) similar to(3.67 +/- 0.05) x 10(-11) s s(-1), computed over an interval of 1960 days.