@spr93; @bil95].

Whether the 1 Hz modulation is created by such instabilities is still an open question. J1808 provides a unique opportunity to study this, since it shows X-ray pulsations that can be observed simultaneously with the aperiodic variability. One of the reasons why the pulsations can play an important role in understanding the mechanism behind the 1 Hz modulation is the pulse behavior observed during the 2002 outburst. A drift of $\sim 0.2$ cycles was observed in the pulse phases of the fundamental frequency (but not in the first overtone), starting and ending in coincidence with the beginning and the end of the fast decay (@bur06). The pulse phase starts to drift in coincidence with the beginning of the fast decay and ends when the re-flares appear. The interpretation of this drift is controversial.

@bur06 concluded that the phase drifts appear in coincidence with the onset of instabilities induced by accretion of matter onto a weakly magnetized star, such as motions of the hot spot on the neutron star surface. @har08 concluded that the observed phase drift might have been due to a motion of the hot spot toward the magnetic pole as the inner accretion disk recedes with 