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

摘要: We studied the X-ray timing and spectral variability of source Sw J1644+57, a candidate for tidal disruption event. have separated long-term trend (an initial decline followed by plateau) from short-term dips in Swift light-curve. Power spectra Lomb-Scargle periodograms hint at possible periodic modulation. By using structure function analysis, we shown that were not random but occurred preferentially time intervals � (2.3,4.5,9) × 10 5 s their higher-order multiples. After plateau epoch, dipping resumed (0.7,1.4) 6 also found spectrum became much softer during each early dip, while outside mildly harder its evolution. propose jet system undergoes precession nutation, which causes collimated core briefly to go out our line sight. The combined effects nutation provide natural explanation peculiar patterns dips. interpret slow hardening baseline flux as transition an extended, optically thin emission region compact, more opaque base jet.