2006/02/28 by Peter Woods, Peter M. Woods, Chryssa Kouveliotou +11 · 4 citations
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Flare #Gamma-ray bursts and supernovae #Magnetar #Magnetosphere #Neutron star #Physics #Plasma #Pulsars and Gravitational Waves Research #Solar flare #Spectral line #astro-ph
paper · pdf · doi:10.1086/507459
published as Astrophys.J.654:470-486,2006 · 37 pages, 8 figures, 8 tables. Accepted for publication in ApJ. To appear in the Oct 20 2006 edition
arxiv created 2006/08/23 · openalex publication_date 2006/12/29 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
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 (|Δν/ν| < 5 × 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 by Mereghetti 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.