Sagittarius A* is the source associated with the 3.5x106 solar mass black hole at the center of our galaxy; its extremely low luminosity (10-9 L_Edd) is a challenge for models accretion physics. The linear polarization of Sgr A*, observable above ~100 GHz, originates just outside the event horizon and provides unique clues about the conditions in the inner accretion flow. Using the Submillimeter Array (SMA) and a multi-frequency polarimeter built for these observations, we have greatly improved the frequency coverage and sensitivity available for polarimetric studies of Sgr A*. We have made the first measurement of Faraday rotation in this source, which restricts the accretion rate to the range 2x10-7 to 2x10-9 Msun/yr. We are also able to detect polarization variability on timescales as short as minutes, indicating rapid changes in the inner accretion flow. In particular, one interesting type of variation may enable future measurements of the black hole spin. Instrument upgrades and a new experimental design should improve our Faraday rotation measurement and allow a search for polarization changes on even shorter timescales this spring. Finally, we have observed a flaring event in Sgr A* across seven decades in frequency through coordinated X-ray/IR/submillimeter observations. The surprising spectral and temporal properties of the flare provide strong constraints on the mechanism responsible for these events.

March 16, 2007
11:00 a.m. MT

Array Operations Center Auditorium

All NRAO employees are invited to attend via video, available in Charlottesville Room 280, Green Bank Room 137 and Tucson 525.

Local Host: Dale Frail