UCL DEPT. OF SPACE & CLIMATE PHYSICS
MULLARD SPACE SCIENCE LABORATORY

Theory Group: Recent Papers

  • Long-term X-ray variability of Swift J1644+57
    Curtis J. Saxton, Roberto Soria, Kinwah Wu, N. Paul M. Kuin,
    2011, Monthly Notices Royal Astronomical Society, submitted
    We studied the X-ray timing and spectral variability of the X-ray source Sw J1644+57, a strong 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 lightcurve. 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. We have also found that the X-ray spectrum became much softer during each dip, while the spectrum outside the dips became harder in its long-term evolution. We propose that the jet in the system undergoes precession and nutation, which has caused 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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