TITLE: GCN GRB OBSERVATION REPORT NUMBER: 2922 SUBJECT: The giant outburst from SGR 1806-20 DATE: 04/12/29 13:18:07 GMT FROM: Dmitry Frederiks at Ioffe Institute E. Mazets, S. Golenetskii, R.Aptekar, D. Frederiks, V. Pal'shin, and T. Cline on behalf of the Konus-Wind team, report: On December 27, 2004, the Konus-Wind instrument detected a giant flare from SGR 1806-20. The flare was preceded by a high emission of recurrent soft bursts. A series of numerous bursts occurred on October 5. On the analogy of the behaviour of SGR 1900+14 before the giant flare on 1998 August 27, it was possible to expect, that SGR 1806-20 is close to generation of a giant flare (GCN 2769). Another series began on December 21 and lasted until the giant flare. These bursts were strong in their flux, exhibiting a well pronounced spectral variability and in some cases unusual spectral features. A record of the giant outburst was triggered by a recurrent burst, which was the strongest in the series. The giant outburst occurred on 142 s after this trigger. The flare started with a very intense initial pulse, resulting in overloading of the detector. It was followed by a long pulsating tail lasted more than 380 s. A measured period of the pulsations is 7.57 ± 0.07 s, indicating its increasing since 2000, when value of 7.49 s was determined in Chandra observations of X-ray persistent flux (Kaplan et al., 2002, ApJ, 564, 935) . Giant outbursts were observed earlier in SGR 0526-66 on 1979 March 5, in SGR 1627-41 on 1998 June 18, in SGR 1900+14 on 1998 August 27. The event of December 27 completes this list for all of well known SGRs. After the outburst, SGR 1806-20 continues to emit recurrent bursts. A determination of energetic and spectral parameters of the outburst will take some time because of a huge intensity of the initial pulse.