James Moran (Harvard-Smithsonian Center for Astrophysics)

Studies of SgrA* at 1.3 mm wavelength: approaching the event horizon - James Moran Colloquium

ATNF Marsfield Lecture Theatre

Abstract

I will discuss polarmetric observations of SgrA* with the SMA, and also VLBI observations of its angular structure. The SMA observations at two frequencies have definitively determined the rotation measure of the source and show that although the Faraday rotation due to the accretion envelope of the associated black hole remains relatively constant, the position angle of the underlying source changes in interesting ways on time scales of an hour or less, which may be indicative of orbital motion near the event horizon. The VLBI observations of SgrA* at 1.3 mm wavelength were carried out with a three element array that included the JCMT/SMA, SMTO and CARMA. At this wavelength the angular resolution was 50 microarcseconds and the expected plasma screen scattering was 25 microarcsecond. The source is clearly resolved and has an equivalent Gaussian size of 37 microarcseconds (scattering removed), or about 2 Schwarzschild diameters. The implication of these measurements and fan plans for future observations will be discussed.