SGRs have spin periods of 5-8 sec with implying magnetic fields of Magnetars! (Thompson & Duncan) There have been 3 Giant Flares of (1979, 1998, 2004) In addition to the spin frequency, all the Giant Flares have also shown much higher frequency QPOs. SGR : 43.5 Hz SGR : 28, 53.5, 88, 155 Hz SGR : 18, 30, 92.5 Hz Woods & Thompson 2004 “ feeble ” Holy cow! SGRs and Giant Flares

SGR ’ s Frequencies Oscillations only seen at a certain phase of the spin Strohmayer & Watts (2005) note that the frequencies scale like for These match Duncan ’ s (1998) estimated shear wave frequencies. Strohmayer & Watts 2005 Rotational phase where 84 Hz signal is strongest 1.5 sec off phase

Simplest Hypothesis: Shear Waves Shear waves easily excited by the crustal deformations (or cracking) during the giant flare Duncan ’ s (1998) estimated frequencies use an interpolation (in gravitational acceleration, g) of McDermott et al. ’ s ( ‘ 88) calculations But frequencies should tell us something about the crust ’ s properties! Depth Density Ocean (liquid) Crust (solid) Core (liquid) Perfect place for shear waves Down

Calculated Frequencies Piro 2005 (astro-ph/ ) Ratio of Following this work, Strohmayer & Watts (2006) found a Hz oscillation!