======================================================================== 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. 13, No. 9 Apr 12, 2001 Recently submitted papers: -------------------------- 1) The motion of stars near the Galactic center: A comparison of the black hole and fermion ball scenarios (Munyaneza & Viollier, ApJ) 2) A Non-Parametric Estimate of the Mass of the Central Black Hole in the Galaxy (Chakrabarty et al., ApJ) 3) X-ray emission from the giant molecular clouds in the Galactic Center region and the discovery of new X-ray sources (Sidoli et al., A&A) ------------------------------------------------------------------------ Email : bilic@physci.uct.ac.za Title : The motion of stars near the Galactic center: A comparison of the black hole and fermion ball scenarios Author(s): Faustin Munyaneza and Raoul D. Viollier Institute: (1) Institute of Theoretical Physics and Astrophysics, Department of Physics, University of Cape Town, Private Bag, Rondebosch 7701, South Africa, fmunyaneza@hotmail.com, viollier@physci.uct.ac.za Paper : ApJ, submitted EPrint : astro-ph/0103466 Abstract: After a discussion of the properties of degenerate fermion balls, we analyze the orbits of the stars S0-1 and S0-2, which have the smallest projected distances to Sgr A^*, in the supermassive black hole as well as in the fermion ball scenarios of the Galactic center. It is shown that both scenarios are consistent with the data, as measured during the last six years by Genzel et al. and Ghez et al. The free parameters of the projected orbit of a star are the unknown components of its velocity v_z and distance z to Sgr A^* in 1995.4, with the z-axis being in the line of sight. We show, in the case of S0-1 and S0-2, that the z-v_z phase- space, which fits the data, is much larger for the fermion ball than for the black hole scenario. Future measurements of the positions or radial velocities of S0-1 and S0-2 could reduce this allowed phase-space and eventually rule out one of the currently acceptable scenarios. This may shed some light into the nature of the supermassive compact dark object, or dark matter in general at the center of our Galaxy. ------------------------------------------------------------------------ Email : dalia@astro.ox.ac.uk Title : A Non-Parametric Estimate of the Mass of the Central Black Hole in the Galaxy Author(s): Dalia Chakrabarty(1,2), Prasenjit Saha(3) Institute: (1) Department of Physics (Astrophysics), University of Oxford, Keble Road, Oxford OX1 3RH, UK (2) Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 3RH, UK (3) Astronomy Unit, School of Mathematical Sciences, Queen Mary and Westfield College, London E1 4NS, UK Paper : ApJ, in press (July 2001) EPrint : astro-ph/0103467 Abstract: We estimate the mass of the central black hole in our Galaxy from stellar kinematical data published by Ghez et al. (1998) and Genzel et al. (2001). For this we develop a method, related to Merritt (1993), for non-parametrically reconstructing the mass profile and the stellar distribution function in the central region of the Galaxy from discrete kinematic data, including velocity errors. Models are searched using the Metropolis algorithm. We assume that the mass distribution is spherical and the stellar velocity distribution is isotropic, and devise a test of this assumption. From proper motions we obtain an enclosed mass of 2.0+/-0.7*10^6 M_o within the inner 0.0044pc, from radial velocities we obtain a mass of 2.2^+1.6_-1.0*10^6M_o within 0.046pc and from three-dimensional velocities we obtain 1.8^+0.4_-0.3*10^6M_o within 0.046pc. ------------------------------------------------------------------------ Email : lsidoli@astro.estec.esa.nl Title : X-ray emission from the giant molecular clouds in the Galactic Center region and the discovery of new X-ray sources Author(s): L. Sidoli(1), S. Mereghetti(2), A. Treves(3), A.N. Parmar(1), R. Turolla(4), and F. Favata(1) Institute: (1) Astrophysics Division, Space Science Department of ESA, ESTEC, Postbus 299, NL-2200 AG Noordwijk, The Netherlands (2) Istituto di Fisica Cosmica G.Occhialini, C.N.R., Via Bassini 15, I-20133 Milano, Italy (3) Universita degli Studi dell'Insubria, Polo di Como, Dipartimento di Scienze Chimiche, Fisiche, e Matematiche, Via Lucini 3, I-22100, Como, Italy (4) Universita di Padova, Dipartimento di Fisica, Via Marzolo 8, I-35131, Padova, Italy Paper : A&A 2001, in press EPrint : astro-ph/0104121 Abstract: We report the results of X-ray (2-10 keV) observations of the giant molecular clouds Sgr B, Sgr C and Sgr D in the Galactic Center region, together with the discovery of the point-like source SAX J1748.2-2808. The data have been obtained with the MECS instrument on the BeppoSAX satellite. The core of Sgr B2 has an X-ray luminosity of 6*10^34 erg s^-1 and its spectrum is characterized by a strong Fe emission line at 6.5 keV with an equivalent width of 2 keV. Faint diffuse X-ray emission is detected from Sgr C and from the SNR G1.05-0.15 (Sgr D). A new, unresolved source with a strong Fe line has been discovered in the Sgr D region. This source, SAX J1748.2-2808, is probably associated with a SiO and OH maser source at the Galactic Center distance. If so, its luminosity is 10^34 erg s^-1. We propose that the X-ray emission from SAX J1748.2-2808 is produced either by protostars or by a giant molecular cloud core. Emission from sources similar to SAX J1748.2-2808 could have an impact on the expected contribution on the observed Fe line emission from the Galactic ridge. ------------------------------------------------------------------------ (Older versions of the Newsflash can be found at the gcnews web-page) ======================================================================== Edited by Angela Cotera Heino Falcke & Sera Markoff (cotera@as.arizona.edu) (hfalcke,smarkoff@mpifr-bonn.mpg.de) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - For Abstract submission please send the (La)Tex file of your paper to gcnews@mpifr-bonn.mpg.de ========================================================================