Volume 445, Number 1, January I 2006
|Page(s)||313 - 321|
|Section||Stellar structure and evolution|
|Published online||13 December 2005|
Two years of INTEGRAL monitoring of the soft gamma-ray repeater SGR 1806-20: from quiescence to frenzy
INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica, via Bassini 15, 20133 Milano, Italy e-mail: firstname.lastname@example.org
2 Space Research Institute, Russian Academy of Sciences, Profsoyuznaya 84/32, 117997 Moscow, Russia
3 Max Planck Institut für Astrophysik, Karl Schwarzschild Str. 1, 85740 Garching bei München, Germany
4 University of California at Berkeley, Space Sciences Laboratory, Berkeley CA 94720-7450, USA
5 European Southern Observatory, Alonso de Cordova 3107, Santiago, Chile
6 External ESA Fellow – Centre d'Étude Spatiale des Rayonnements (CESR), avenue du Colonel-Roche 9, 31028 Toulouse Cedex 4, France
7 Danish National Space Center (DNSC), Juliane Maries Vej 30, 2100 Copenhagen, Danemark
8 INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica, via Fosso del Cavaliere 100, 00133 Roma, Italy
9 Sabanci University, Orhanli-Tuzla, Istanbul, Turkey
10 Astronomical Institute “Anton Pannekoek”, University of Amsterdam and Center for High-Energy Astrophysics, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
11 National Space Science and Technology Center, 320 Sparkman Drive, Huntsville, AL 35805, USA
12 NASA Marshall Space Flight Center, XD 12, Huntsville, AL 35812, USA
13 INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica, via Gobetti 101, 40129 Bologna, Italy
14 ESA-ESTEC, RSSD, Keplerlaan 1, 2201 AZ Nordwijk, The Netherlands
15 Department of Physics, University of Manchester, Sackville Street, PO Box 88, Manchester M60 1QD, UK
Accepted: 29 August 2005
SGR 1806–20 has been observed for more than 2 years with the INTEGRAL satellite. In this period the source went from a quiescent state into a very active one culminating in a giant flare on December 27, 2004. Here we report on the properties of all the short bursts detected with INTEGRAL before the giant flare. We derive their number-intensity distribution and confirm the hardness-intensity correlation for the bursts found by Götz et al. (2004a, A&A, 417, L45). Our sample includes a very bright outburst that occurred on October 5, 2004, during which over one hundred bursts were emitted in 10 minutes, involving an energy release of erg. We present a detailed analysis of it and discuss our results in the framework of the magnetar model.
Key words: gamma rays: bursts / gamma rays: observations / stars: pulsars: general / stars: pulsars: individual: SGR 1806-20
© ESO, 2005
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