A polarized infrared flare from Sagittarius A* and the signatures of orbiting plasma hotspots

In this article we summarize and discuss the infrared, radio and X-ray emission from the supermassive black hole in the Galactic Centre, SgrA * . We include new results from nearinfrared polarimetric imaging observations obtained on 2006 May 31. In that night, a strong flare in K s band (2.08 m) reaching top fluxes of 16 mJy could be observed. This flare was highly polarized (up to 40 per cent) and showed clear substructure on a time-scale of 15 min, including a swing in the polarization angle of about 70 . For the first time we were able to observe both polarized flux and short-time variability, with high significance in the same flare event. This result adds decisive information to the puzzle of the SgrA * activity. The observed polarization angle during the flare peak is the same as observed in two events in 2004 and 2005. Our observations strongly support the dynamical emission model of a decaying plasma hotspot orbiting SgrA * on a relativistic orbit. The observed polarization parameters and their variability with time might allow to constrain the orientation of accretion disc and spin axis with respect to the Galaxy.