Rapid X-ray oscillations in magnetar giant flares

Anna L Watts

NASA Goddard Space Flight Center


Israel and co-authors recently reported the detection of high frequency QPOs in the December 2004 giant flare from the magnetar SGR 1806-20. They suggested that the QPOs may have their origin in torsional vibrations of the neutron star crust. In this talk we report the discovery of similar high frequency oscillations in the August 1998 giant flare of SGR 1900+14. We discuss our findings in the light of the torsional mode model and show that if the stars have similar masses then the magnetic field of SGR 1806-20 must be about twice as large as that of SGR 1900+14, which is broadly consistent with magnetic field estimates from pulse timing. We also show how detailed mode identifications could lead to constraints on the nuclear equation of state.


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