@article{9f502b119ff94d73b6ba32c90a1ff687,
title = "The Discovery of rapid X-ray oscillations in the tail of the SGR 1806-20 hyperflare",
abstract = "We have discovered rapid quasi-periodic oscillations (QPOs) in RXTE/PCA measurements of the pulsating tail of the 2004 December 27 giant flare of SGR 1806-20. QPOs at ∼92.5 Hz are detected in a 50 s interval starting 170 s after the onset of the giant flare. These QPOs appear to be associated with increased emission by a relatively hard unpulsed component and are seen only over phases of the 7.56 s spin period pulsations away from the main peak. QPOs at ∼18 and ∼30 Hz are also detected ∼200-300 s after the onset of the giant flare. This is the first time that QPOs are unambiguously detected in the flux of a soft gamma-ray repeater or any other magnetar candidate. We interpret the highest QPOs in terms of the coupling of toroidal seismic modes with Alfv{\'e}n waves propagating along magnetospheric field lines. The lowest frequency QPO might instead provide indirect evidence on the strength of the internal magnetic field of the magnetar.",
keywords = "Pulsars: Individual (SGR 1806-20), Stars: Flare, Stars: Neutron, Stars: Oscillations, X-rays: Bursts",
author = "Israel, {G. L.} and T. Belloni and L. Stella and Y. Rephaeli and Gruber, {D. E.} and P. Casella and S. Dall'Osso and N. Rea and M. Persic and Rothschild, {R. E.}",
note = "Funding Information: This work is partially supported by Agenzia Spaziale Italiana (ASI), Ministero dell{\textquoteright}Istruzione, Universit{\`a} e Ricerca Scien-tifica e Tecnologica (MIUR-COFIN), and Istituto Nazionale di Astrofisica (INAF) grants. Work at UCSD has been supported by a NASA grant. We thank an anonymous referee for his/her valuable suggestions.",
year = "2005",
month = jul,
day = "20",
doi = "10.1086/432615",
language = "אנגלית",
volume = "628",
pages = "L53--L56",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "1 II",
}