Two years of INTEGRAL monitoring of the soft gamma-ray repeater SGR 1806-20: from quiescence to frenzy
Hurley, K.; Sunyaev, R.; Götz, D.; Mereghetti, S.; Kouveliotou, C.; van der Klis, M.; von Kienlin, A.; Molkov, S.; Ubertini, P.; Mirabel, I. F.; Lund, N.; Feroci, M.; Brandt, S.; Weidenspointner, G.; Winkler, C.; Woods, P. M.; Pizzichini, G.; Göğüş, E.; del Santo, M.
Italy, Russia, Germany, United States, Chile, France, Denmark, Turkey, Netherlands, United Kingdom
Abstract
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 3× 1042 erg. We present a detailed analysis of it and discuss our results in the framework of the magnetar model.