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Session 119 - Gamma Ray Bursts.
Oral session, Saturday, January 10
International Ballroom Center,

[119.08] QPOs in Soft Gamma Repeaters: Evidence for the Magnetar Model

R. C. Duncan (U. Texas at Austin)

We consider the nature of the 30 Hz oscillations recently detected from SGR 1806-20 by RXTE. We show that such oscillations are naturally predicted by the magnetar model of Soft Gamma Repeaters (SGRs). In the magnetar model, the star has an ultra-strong magnetic field which drives crust fractures, observable as bursts. We explain how the 30 Hz oscillations are excited and damped, and how they are involved in triggering bursts. We estimate excitation and damping efficiencies and rates, as well as the amplitude of the mode in SGR 1806-20. We also propose a new explanation for the "pre-glow" found by XTE: rising humps of faint X-ray emission which precede bright bursts. In addition, we explain the long, faint emissions that are seen accompanying bursting episodes. These long, faint emissions have similar spectra and total energies as bright bursts, but lower luminosities and longer durations by several orders of magnitude. In conclusion, we argue that these new RXTE observations together constitute a "smoking gun" for the magnetar model.

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