High-resolution Observations of OH(1720 MHz) Masers, Toward the Galactic Center

F. Yusef-Zadeh(1), D. A. Roberts(2), W. M. Goss(3), D.A. Frail(3), A. J. Green(4)

(1) Department of Physics and Astronomy, Northwestern University, Evanston, Il. 60208 (zadeh@nwu.edu)
(2) NCSA, 405 N. Mathews Ave, Urbana, IL 61801 (dougr@ncsa.uiuc.edu)
(3) National Radio Astronomy Observatory, P.O. Box 0, Socorro, New Mexico 87801 (mgoss@aoc.nrao.edu), (dfrail@aoc.nrao.edu)
(4) University of Sydney, School of Physics, A28, Sydney, NSW 2006 Australia (agreen@physics.usyd.edu.au)

Paper: ApJ, in press

EPrint Server: astro-ph/9809279


High-resolution VLA observations of 1720 MHz OH maser emission from Sgr A East and the circumnuclear disk with spatial and spectral resolutions of ~ 2\dasec5 * 1\dasec3 and 0.27 km/sec are reported. This follow-up observational study focuses on the recent discovery of a number of such OH maser features and their intense circularly polarized maser lines detected toward these Galactic center sources. The 1720 MHz maser line of OH arises from collisionally excited gas behind a C-type shock and is an important diagnostic of the interaction process that may occur between molecular clouds and associated X-ray emitting shell-type supernova remnants. The present observations have confirmed that the observed Stokes V signal is due to Zeeman splitting and that the OH masers are angularly broadened by the scattering medium toward the Galactic center. The scale length of the magnetic field fluctuations in the scattering medium toward the Galactic center is estimated to be greater than 0.1-0.2 pc using the correlation of the position angles of the scatter-broadened maser spots. In addition, the kinematics of the maser spots associated with Sgr A East are used to place a 5 pc displacement between this extended radio structure and the Galactic center.

Preprints available from the authors at ZADEH@OSSENU.ASTRO.NWU.EDU , or the raw TeX (no figures) if you click here.

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