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Quasi-periodic oscillations (QPOs) detected in the 2004 giant flare from SGR1806-20 are often interpreted as global magneto-elastic oscillations of theneutron star. There is, however, a large discrepancy between theoreticalmodels, which predict that the highest frequency oscillations should die outrapidly, and the observations, which suggested that the highest-frequencysignals persisted for ~100s in X-ray data from two different spacecraft. Thisdiscrepancy is particularly important for the high-frequency QPO at ~625 Hz.However, previous analyses did not systematically test whether the signal couldalso be there in much shorter data segments, more consistent with thetheoretical predictions. Here, we test for the presence of the high-frequencyQPO at 625 Hz in data from both the Rossi X-ray Timing Explorer (RXTE) and theRamaty High Energy Solar Spectroscopic Imager (RHESSI) systematically both inindividual rotational cycles of the neutron star, as well as averaged overmultiple successive rotational cycles at the same phase. We find that the QPOin the RXTE data is consistent with being only present in a single cycle, for ashort duration of ~0.5s, whereas the RHESSI data are as consistent with ashort-lived signal that appears and disappears as with a long-lived QPO. Takentogether, this data provides evidence for strong magnetic interaction betweenthe crust and the core.

astrophysical journal/the astrophysical journal

Intermittency and Lifetime of the 625 Hz QPO in the 2004 Hyperflare from  the Magnetar SGR 1806-20 as evidence for magnetic coupling between the crust  and the core