RXTE observation of recent flaring activity from the transient X-ray pulsar 2S 1553−542


  • Mayukh Pahari,

    Corresponding author
    1. Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India
    2. Department of Physics, University of Pune, Pune 411007, India
    3. National Centre for Radio Astrophysics, Pune 411007, India
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  • Sabyasachi Pal

    Corresponding author
    1. ICRAR, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia
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E-mail: mp@tifr.res.in (MP); sabyasachi.pal@icrar.org (SP)


We summarize the analysis of observations made by the Rossi X-ray Timing Explorer and the Swift/Burst Alert Telescope at the time of the recent flaring activity of the transient X-ray pulsar 2S 1553−542. The binary system is characterized by the projected semimajor axis ax sin  i of 168 ± 18 light-seconds, the binary orbital period Porb of 29.56 ± 0.53 d and the X-ray mass function fx(M) of 5.3 ± 1.2 M. We also found Pspin= 9.2829 ± 0.0003 s with inline image s s−1, i.e. a spin-up rate of inline image yr−1. The spin period is found to decrease more slowly than that of most other X-ray pulsars. As the flare decays with time, the structure and X-ray counts in the pulse profile showed considerable variability. However, no significant structural variability is seen in single-peaked pulse profiles in different energy bands. Pulsed fraction decreases with the decay of the flare but its value at different energy bands showed a discontinuity. Using X-ray spectroscopy at different orbital cycles, we have detected the presence of the Fe Kα emission line in the spectra with a minimum significance of 3σ. Apart from a consistent increase in blackbody temperature, other spectral parameters are found to be stable throughout orbital cycles. From detailed spectral and timing analysis, we concluded that the X-ray flare is spectrally hard and we confirmed the nature of the compact object as a transient, accretion-powered, spin-up X-ray pulsar with a Be-type companion.