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      https://www.ias.ac.in/article/fulltext/joaa/028/04/0175-0184

    • Keywords

       

      Accretion, accretion disks; binaries: general; stars: individual (4U 1626-67); stars: neutron; X-rays: stars.

    • Abstract

       

      We report here results from a new search for orbital motion of the accretion powered X-ray pulsar 4U 1626-67 using two different analysis techniques. X-ray light curve obtained with the Proportional Counter Array of the Rossi X-ray Timing Explorer during a long observation carried out in February 1996, was used in this work. The spin period and the local period derivative were first determined from the broad 2–60 keV energy band light curve and these were used for all subsequent timing analysis. In the first technique, the orbital phase dependent pulse arrival times were determined for different trial orbital periods in the range of 500 to 10,000 s. We have determined a 3𝜎 upper limit of 13 lt-ms on the projected semimajor axis of the orbit of the neutron star for most of the orbital period range, while in some narrow orbital period ranges, covering about 10% of the total orbital period range, it is 20 lt-ms. In the second method, we have measured the pulse arrival times at intervals of 100 s over the entire duration of the observation. The pulse arrival time data were used to put an upper limit on any periodic arrival time delay using the Lomb–Scargle periodogram. We have obtained a similar upper limit of 10 lt-ms using the second method over the orbital period range of 500–10,000 s. This puts very stringent upper limits for the mass of the compact object except for the unlikely case of a complete face-on orientation of the binary system with respect to our line-of-sight. In the light of this measurement and the earlier reports, we discuss the possibility of this system being a neutron star with a supernovae fall-back accretion disk.

    • Author Affiliations

       

      Chetana Jain1 Biswajit Paul2 Kaustubh Joshi3 Anjan Dutta1 Harsha Raichur2 4

      1. Department of Physics and Astrophysics, University of Delhi, Delhi 110 007, India.
      2. Raman Research Institute, Sadashivnagar, C. V. Raman Avenue, Bangalore 560 080, India.
      3. Department of Electrical Engineering, Indian Institute of Technology – Bombay, Powai, Mumbai 400 076, India.
      4. Joint Astronomy Programme, Indian Institute of Science, Bangalore 560 012, India.
    • Dates

       
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