Polarized Near-infrared Flares from Sgr A*: Orbiting Hotspot?

I present the results of a near-infrared monitoring
of Sgr A*, the super-massive black hole at the center
of our Galaxy. Sgr A* was observed continuously for
about four hours on 28 May 2008, using the near-infrared
camera CIAO and the 36-element AO system on the Subaru
telescope. We observed three flares in 220 min monitoring.
Clear variations in the degree and position angle of
polarization were also detected: an increase of the
degree of polarization of about 20 %, and a swing of
the position angle of ~60deg - 70deg in the declining
phase of the flares. The correlation between the flux
and the degree of polarization suggests that the flare
emission comes from hotspot(s) orbiting Sgr A*. Comparison
with calculations in the literature gives a constraint
to the inclination angle theta of the orbit of the hotspot
around Sgr A*, as 0<theta<45deg (theta=0: edge-on).