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

S. Trippe,1, T. Paumard,1, T. Ott,1, S. Gillessen,1 F. Eisenhauer,1 F. Martins1 and R. Genzel1,2

1) Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, D-85741 Garching, Germany, 2) Department of Physics, University of California, CA 94720, Berkeley, USA

Paper: MNRAS, Nov 2006, in press

EPrint Server: astro-ph/0611737


Abstract:

In this article we summarise and discuss the infrared, radio, and X-ray emission from the supermassive black hole in the Galactic Centre, SgrA*. We include new results from near-infrared polarimetric imaging observations obtained on May 31st, 2006. In that night, a strong flare in Ks band (2.08 micron ) reaching top fluxes of 16 mJy could be observed. This flare was highly polarised (up to 40 %) and showed clear sub-structure on a time scale of 15 minutes, including a swing in the polarisation angle of about 70 degrees. For the first time we were able to observe both polarised 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 polarisation 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 polarisation parameters and their variability with time might allow to constrain the orientation of accretion disc and spin axis with respect to the Galaxy.


Preprints available from the authors at trippe@mpe.mpg.de , or the raw TeX (no figures) if you click here.

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