7 mm lambda VLBA Observations of Sagittarius A*

Geoffrey C. Bower, & Donald C. Backer

(1) Max Planck Institut für Radioastronomie, Auf dem Hügel 69, D 53121 Bonn Germany
(2) Astronomy Department & Radio Astronomy Laboratory, University of California, Berkeley, CA 94720

Paper: ApJL accepted

Weblink: http://www.aoc.nrao.edu/mpivlb/bower/publications.html


Abstract:

We present 7 mm lambda VLBA observations of the compact nonthermal radio source in the Galactic Center, Sgr A*. These observations confirm the hypothesis that the image of Sgr A* is a resolved elliptical Gaussian caused by the scattering of an intervening thermal plasma. The measured major axis of Sgr A* is 0.76 +/- 0.04 mas, consistent with the predicted scattering size of 0.67 +/- 0.03. We find an axial ratio of 0.73 +/- 0.10 and a position angle of 77o +/- 7o. These results are fully consistent with VLBI observations at longer wavelengths and at 3 mm lambda . We find no evidence for any additional compact structure to a limit of 35 mJy. The underlying radio source must be smaller than 4.1 AU for a galactocentric distance of 8.5 kpc. This result is consistent with the conclusion that the radio emission from Sgr A* results from synchrotron or cyclo-synchrotron radiation of gas in the vicinity of a black hole with a mass near 10^6 Mo.


Preprints available from the authors at gbower@mpifr-bonn.mpg.de , or the raw TeX (no figures) if you click here.

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