The prelude to and aftermath of the giant flare of 2004 December 27: persistent and pulsed X-Ray properties of SGR 1806-20 from 1993 to 2005
Woods, Peter M. and Kouveliotou, Chryssa and Finger, Mark H. and Göğüş, Ersin and Wilson, Colleen A. and Patel, Sandeep K. and Hurley, Kevin and Swank, Jean H. (2007) The prelude to and aftermath of the giant flare of 2004 December 27: persistent and pulsed X-Ray properties of SGR 1806-20 from 1993 to 2005. The Astrophysical journal, 654 (1). pp. 470-486. ISSN 0004-637X
Official URL: http://dx.doi.org/10.1086/507459
We report on the evolution of key spectral and temporal parameters of SGR 1806 - 20 prior to and following the highly energetic giant flare of 2004 December 27. Using RXTE, we track the pulse frequency of the SGR and find that the spin-down rate varied erratically in the months before and after the flare. Contrary to the giant flare in SGR 1900+14, we find no evidence for a discrete jump in spin frequency at the time of the December 27th flare (\Delta nu/nu\ < 5 x 10(-6)). In the months surrounding the flare, we find a strong correlation between pulsed flux and torque consistent with the model for magnetar magnetosphere electrodynamics proposed by Thompson et al. As with the flare in SGR 1900+14, the pulse morphology of SGR 1806 - 20 changes drastically following the flare. Using Chandra and other publicly available imaging X-ray detector observations, we construct a spectral history of SGR 1806 - 20 from 1993 to 2005. The usual magnetar persistent emission spectral model of a power law plus a blackbody provides an excellent fit to the data. We confirm the earlier finding byMereghetti et al. of increasing spectral hardness of SGR 1806 - 20 between 1993 and 2004. However, our results indicate significant differences in the temporal evolution of the spectral hardening. Rather than a direct correlation between torque and spectral hardness, we find evidence for a sudden torque change that preceded a gradual hardening of the energy spectrum on a timescale of years. Interestingly, the spectral hardness, spin-down rate, phase-averaged flux, and pulsed flux of SGR 1806 - 20 all peak months before the flare epoch.
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