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A. Ibrahim (NASA/GSFC & GWU), J. Swank (NASA/GSFC), W. Parke (GWU)
Evidence of magnetars associated with Soft Gamma Repeaters and Anomalous X-Ray Pulsars has accumulated over the years, including the extremely energetic and short burst durations, the long spin period and high spin-down, and also lack of evidence for a binary companion of a remnant accretion disk. Nevertheless, the determination of magnetars' most important parameter, the magnetic field strength, remained indirect for the past decade. With the Proportional Counter Array on board the Rossi X-ray Timing Explorer, we have recently discovered a 5 keV absorption feature in the burst spectra of SGR 1806-20. Consistent with proton cyclotron resonance, the feature provided a direct measurement of a magnetar-strength field and implied constraints on the mass and radius of the source. Here we outline our result and present further analysis and interpretation of new data.
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Bulletin of the American Astronomical Society,
© 2003. The American Astronomical Soceity.