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Title: SALT observation of X-ray pulse reprocessing in 4U 1626-67
Authors: Raman, Gayathri
Paul, Biswajit
Bhattacharya, D.
Mohan, Vijay
Issue Date: 11-May-2016
Publisher: Oxford University Press for The Royal Astronomical Society
Citation: Monthly Notices of the Royal Astronomical Society, 2016, Vol. 458, p 1302-1310
Abstract: We investigate optical reprocessing of X-rays in the low-mass X-ray binary (LMXB) pulsar 4U 1626−67 in its current spin-up phase using observations with Southern African Large Telescope (SALT), near-simultaneous observations with Swift-X-ray Telescope and non-simultaneous RXTE-Proportional Counter Array (PCA) observations and present the results of timing analysis. Using SALT observations carried out on 2014 March 5 and 6, we detect some interesting reprocessing signatures. We detect a weak optical quasiperiodic oscillation (QPO) in the power density spectrum on March 5 at 48 mHz with a fractional rms of 3.3 per cent in spite of the fact that source shows no corresponding X-ray QPO in the spin-up phase. In the light curve obtained on March 5, we detect a coherent pulsation at the spin period of ∼7.677 s. A previously known, slightly down-shifted side-band is also detected at 129.92 mHz. The frequency spacing between main pulse and this side-band is different from earlier observations, though the statistical significance of the difference is limited. The light curve of March 6 displays short time-scale variability in the form of flares on time-scales of a few minutes. Folded pulse profiles resulting from data of this night show an interesting trend of pulse peak drifting. This drift could be due to (i) rapid changes in the reprocessing agent, like orbital motion of an accretion disc warp around the neutron star, or (ii) intrinsic pulse phase changes in X-rays. We also examine some X-ray light curves obtained with RXTE-PCA during 2008–2010 for pulse shape changes in short time-scales during X-ray flares.
Description: Open Access
ISSN: 0035-8711
1365-2966 - (online)
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Copyright: 2016 The authors & the Royal Astronomical Society.
Appears in Collections:Research Papers (A&A)

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