======================================================================== G C N E W S * Newsflash * - The Newsletter for Galactic Center Research - gcnews@aoc.nrao.edu http://www.aoc.nrao.edu/~gcnews ======================================================================== Vol. 27, No. 9 Oct 19, 2007 Recently submitted papers: -------------------------- 1) Getting a kick out of the stellar disk(s) in the galactic center (Perets & Alexander, IAU-246) 2) Simultaneous H.E.S.S. and Chandra observations of Sgr A* during an X-ray flare (Hinton et al., proceedings) 3) Low angular momentum accretion flow model of Sgr A* activity (Czerny et al., proceedings) 4) Three-Dimensional Observations of H_2 Emission, around Sgr A East, - I. Structure in the Central 10 Parsecs of Our Galaxy (Lee et al., ApJ) ------------------------------------------------------------------------ Email : hagai.perets@weizmann.ac.il Title : Getting a kick out of the stellar disk(s) in the galactic center Author(s): Hagai B. Perets, Gabor Kupi \& Tal Alexander Paper : IAU-246 proceedings Abstract: Recent observations of the Galactic center revealed a nuclear disk of young OB stars, in addition to many similar outlying stars with higher eccentricities and/or high inclinations relative to the disk (some of them possibly belonging to a second disk). Binaries in such nuclear disks, if they exist in non-negligible fractions, could have a major role in the evolution of the disks through binary heating of this stellar system. We suggest that interactions with/in binaries may explain some (or all) of the observed outlying young stars in the Galactic center. Such stars could have been formed in a disk, and later on kicked out from it through binary related interactions, similar to ejection of high velocity runaway OB stars in young clusters throughout the galaxy. ------------------------------------------------------------------------ Email : j.a.hinton@leeds.ac.uk Title : Simultaneous H.E.S.S. and Chandra observations of Sgr A* during an X-ray flare Author(s): Jim Hinton(1), Matthieu Vivier(2), Rolf B\"uhler(3), Gerd P\"uhlhofer(4), Stefan Wagner(4) for the H.E.S.S. Collaboration Paper : Proc ICRC 2007 Abstract: The rapidly varying non-thermal X-ray emission observed from Sgr A* points to particle acceleration taking place close to the supermassive black hole. The TeV gamma -ray source HESS J1745-290 is coincident with Sgr A* and may be closely related to the X-ray emission. Simultaneous X-ray and TeV observations are required to elucidate the relationship between these two objects. Here we report on joint H.E.S.S./Chandra observations in July 2005, during which an X-ray flare was detected. Despite a factor >10 increase in the X-ray flux of Sgr A*, no evidence is found for an increase in the TeV gamma -ray flux. We find that an increase of the gamma -ray flux of a factor 2 or greater can be excluded at a confidence level of 99%. This finding disfavours scenarios in which the bulk of the gamma -ray emission observed is produced close to Sgr A*. ------------------------------------------------------------------------ Email : monikam@physics.unlv.edu Title : Low angular momentum accretion flow model of Sgr A* activity Author(s): Bozena Czerny(1) Monika Moscibrodzka(1) Daniel Proga(2) Tapas K. Das(3) and Aneta Siemiginowska(4) Institute: (1) Copernicus Astronomical Center, Bartycka 18, 00 710 Warsaw, Poland (2) Department of Physics, University of Nevada, Las Vegas, NV 89154, USA (3) Harish Chandra Research Institute, Allahabad-211 019, India (4) Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge MA 02138, USA Paper : proceedings Abstract: Sgr A* is a source of strongly variable emission in several energy bands. It is generally agreed that this emission comes from the material surrounding the black hole which is either falling in or flowing out. The activity must be driven by accretion but the character of accretion flow in this object is an open question. We suggest that the inflow is dominated by the relatively low angular momentum material originating in one of the nearby group of stars. Such material flows in directly towards the black hole up to the distance of order of ten Schwarzschild radii or less, where it hits the angular momentum barrier which leads naturally to a flow variability. We study both the analytical and the numerical solutions for the flow dynamics, and we analyze the radiation spectra in both cases using the Monte Carlo code to simulate the synchrotron, bremsstrahlung and the Compton scattering. Our model roughly reproduces the broad band spectrum of Sgr A* and its variability if we allow for a small fraction of energy to be converted to non-thermal population of electrons. It is also consistent (for a range of viewing angles) with the strong constraints on the amount of circumnuclear material imposed by the measurements of the Faraday rotation. ------------------------------------------------------------------------ Email : soojongpak@gmail.com Title : Three-Dimensional Observations of H_2 Emission, around Sgr A East, - I. Structure in the Central 10 Parsecs of Our Galaxy Author(s): Sungho Lee(1), Soojong Pak(2), Minho Choi(1), Christopher J. Davis(3), T. R. Geballe(4), Robeson M. Herrnstein(5,6), Paul T. P. Ho(5,7), Y. C. Minh(1,7), and Sang-Gak Lee(8) Institute: (1) Korea Astronomy and Space Science Institute, 61-1 Hwaam-dong, Yuseong-gu, Daejeon 305-348, South Korea (2) Department of Astronomy and Space Science, Kyung Hee University, Yongin-si, Gyeonggi-do 446-701, South Korea; Corresponding Author, soojong@khu.ac.kr (3) Joint Astronomy Centre, University Park, 660 North A'ohoku Place, Hilo, HI 96720 (4) Gemini Observatory, 670 N. A'ohoku Place, Hilo, HI 96720 (5) Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (6) Department of Astronomy, Columbia University, 550 West 120th St. New York, NY 10027 (7) Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei, 106 Taiwan (8) Department of Astronomy, Seoul National University, Kwanak-gu, Seoul 151-742, South Korea Paper : ApJ, Jan 2008, in press EPrint : 0710.0979 Abstract: We have obtained velocity-resolved spectra of the H_2 1-0 S(1) ( lambda = 2.1218 micron ) emission line at 2'' angular resolution (or 0.08 pc spatial resolution) in four regions within the central 10 pc of the Galaxy where the supernova-like remnant Sgr A East is colliding with molecular clouds. To investigate the kinematic, physical, and positional relationships between the important gaseous components in the center, we compared the H_2 data cube with previously published NH_3 data. The projected interaction-boundary of Sgr A East is determined to be an ellipse with its center offset 1.5 pc from Sgr A* and dimensions of 10.8 pc * 7.6 pc. This H_2 boundary is larger than the synchrotron emission shell but consistent with the dust ring which is believed to trace the shock front of Sgr A East. Since Sgr A East is driving shocks into its nearby molecular clouds, we can determine their positional relationships using the shock directions as indicators. As a result, we suggest a revised model for the three-dimensional structure of the central 10 pc. The actual contact between Sgr A East and all of the surrounding molecular material, including the circum-nuclear disk and the southern streamer, makes the hypothesis of infall into the nucleus and feeding of Sgr A* very likely. ------------------------------------------------------------------------ (Older versions of the Newsflash can be found at the gcnews web-page) ======================================================================== Edited by Sera Markoff, Loránt Sjouwerman, Joseph Lazio, Cornelia Lang, Rainer Schödel, Masaaki Sakano, Feng Yuan - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - For Abstract submission please follow the instructions which are at http://www.aoc.nrao.edu/~gcnews/home/submission.shtml ========================================================================