======================================================================== G C N E W S * Newsflash * - The Newsletter for Galactic Center Research - gcnews@mpifr-bonn.mpg.de http://www.mpifr-bonn.mpg.de/gcnews ======================================================================== Vol. 10, No. 6 Jul 16, 1999 Recently submitted papers: -------------------------- Email : gbower@vegas.aoc.nrao.edu Title : Detection of Circular Polarization in the Galactic Center Black Hole Candidate Sagittarius A* Author(s): Geoffrey C. Bower(1), Heino Falcke(2,3) \& Donald C. Backer(4) Institute: (1) National Radio Astronomy Observatory, P.O. Box O, 1003 Lopezville, Socorro, NM 87801; gbower@nrao.edu (2) Max Planck Institut fuer Radioastronomie, Auf dem Huegel 69, D 53121 Bonn Germany; hfalcke@mpifr-bonn.mpg.de (3) Steward Observatory, The University of Arizona, Tucson, AZ 85721 (4) Astronomy Department \& Radio Astronomy Laboratory, University of California, Berkeley, CA 94720; dbacker@astro.berkeley.edu Paper : accepted in ApJL Weblink : http://www.nrao.edu/~gbower/publications.html EPrint : astro-ph/9907215 (after 7/19/1999) Abstract: We report here the detection of circular polarization in the Galactic Center black hole candidate, Sagittarius A*. The detection was made at 4.8 GHz and 8.4 GHz with the Very Large Array. We find that the fractional circular polarization at 4.8 GHz is m_c=-0.36 +/- 0.05% and that the spectral index of the circular polarization is alpha =-0.6 +/- 0.3 (m_c \propto nu ^ alpha ). The systematic error in m_c is less than 0.04% at both frequencies. In light of our recent lower limits on the linear polarization in Sgr A*, this detection is difficult to interpret with standard models. We consider briefly whether scattering mechanisms could produce the observed polarization. Detailed modeling of the source and the scattering medium is necessary. We propose a simple model in which low energy electrons reduce linear polarization through Faraday depolarization and convert linear polarization into circular polarization. Circular polarization may represent a significant new parameter for studying the obscured centimeter wavelength radio source in Sgr A*. ------------------------------------------------------------------------ Email : clang@zia.aoc.NRAO.EDU Title : Radio Detections of Stellar Winds from the Pistol Star and Other Stars in the Galactic Center Quintuplet Cluster Author(s): Cornelia C. Lang(1,2), Don F. Figer(2), W.M. Goss(1), and Mark Morris(2) Institute: (1) National Radio Astronomy Observatory, Box 0, Socorro, NM 87801, email: clang@nrao.edu (2) Division of Astronomy, 8371 Math Sciences Building, Box 951562, University of California at Los Angeles, LA, CA 90095-1562 Paper : to appear in the Astronomical Journal, Nov 1999 EPrint : astro-ph/9907176 Abstract: VLA images of the Sickle and Pistol H II regions near the Galactic center at 3.6 and 6 cm reveal six point sources in the region where the dense Quintuplet stellar cluster is located. The spectral indices of five of these sources between 6 cm and 3.6 cm have values of alpha = +0.5 to +0.8, (where S_ nu \propto nu^alpha ), consistent with the interpretation that the radio sources correspond to ionized stellar winds of the massive stars in this cluster. The radio source associated with the Pistol Star shows alpha=-0.4\p0.2, consistent with a flat or slightly non-thermal spectrum. (Older versions of the Newsflash can be found at the gcnews web-page) ======================================================================== Edited by Angela Cotera Heino Falcke (cotera@ipac.caltech.edu) (hfalcke@mpifr-bonn.mpg.de) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - For Abstract submission please send the (La)Tex file of your paper to gcnews@mpifr-bonn.mpg.de ========================================================================