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    Long-term X-ray variability of Swift J1644+57

    219009_68361_70398_publishedversion.pdf (7.585Mb)
    Access Status
    Open access
    Authors
    Saxton, C.
    Soria, Roberto
    Wu, K.
    Kuin, N.
    Date
    2012
    Type
    Journal Article
    
    Metadata
    Show full item record
    Citation
    Saxton, C. and Soria, R. and Wu, K. and Kuin, N. 2012. Long-term X-ray variability of Swift J1644+57. Monthly Notices of the Royal Astronomical Society. 422: pp. 1625-1639.
    Source Title
    Monthly Notices of the Royal Astronomical Society
    DOI
    10.1111/j.1365-2966.2012.20739.x
    ISSN
    1365-2966
    School
    Curtin Institute of Radio Astronomy (Physics)
    Remarks

    This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society, ©: 2012, the authors and the Royal Astronomical Society. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

    URI
    http://hdl.handle.net/20.500.11937/34811
    Collection
    • Curtin Research Publications
    Abstract

    We studied the X-ray timing and spectral variability of the X-ray source Sw J1644+57, a candidate for a tidal disruption event. We have separated the long-term trend (an initial decline followed by a plateau) from the short-term dips in the Swift light curve. Power spectra and Lomb–Scargle periodograms hint at possible periodic modulation. By using structure function analysis, we have shown that the dips were not random but occurred preferentially at time intervals ≈(2.3, 4.5, 9) × 105 s and their higher order multiples. After the plateau epoch, dipping resumed at ≈(0.7, 1.4) × 106 s and their multiples. We have also found that the X-ray spectrum became much softer during each of the early dips, while the spectrum outside the dips became mildly harder in its long-term evolution. We propose that the jet in the system undergoes precession and nutation, which causes the collimated core of the jet briefly to go out of our line of sight. The combined effects of precession and nutation provide a natural explanation for the peculiar patterns of the dips. We interpret the slow hardening of the baseline flux as a transition from an extended, optically thin emission region to a compact, more opaque emission core at the base of the jet.

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