======================================================================== 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. 11 Nov 29, 2007 Recently submitted papers: -------------------------- 1) The proper motion of the Arches cluster with Keck Laser-Guide Star Adaptive Optics (Stolte et al., ApJ) 2) X-Ray Observations of the Galactic Center with Suzaku (Koyama et al., AN) 3) A Time-Variable X-Ray Echo: Indications of a Past Flare of the Galactic-Center Black Hole (Koyama et al., PASJ) ------------------------------------------------------------------------ Email : astolte@astro.UCLA.EDU Title : The proper motion of the Arches cluster with Keck Laser-Guide Star Adaptive Optics Author(s): A. Stolte(1), A. M. Ghez(1,2), M. Morris(1), J. R. Lu(1), W. Brandner(1,3), K. Matthews(4) Institute: (1) Division of Astronomy and Astrophysics, UCLA, Los Angeles, CA 90095-1547 (2) Institute of Geophysics and Planetary Physics, UCLA, Los Angeles, CA 90095 (3) Max-Planck-Institut for Astronomy, Koenigstuhl 17, 69117 Heidelberg, Germany (4) Caltech Optical Observatories, California Institute of Technology, MS 320-47, Pasadena, CA 91225 Paper : ApJ, March 2008, in press EPrint : 0706.4133 Abstract: We present the first measurement of the proper motion of the young, compact Arches cluster near the Galactic center from near-infrared adaptive optics (AO) data taken with the recently commissioned laser-guide star (LGS) at the Keck 10-m telescope. The excellent astrometric accuracy achieved with LGS-AO provides the basis for a detailed comparison with VLT/NAOS-CONICA data taken 4.3 years earlier. Over the 4.3 year baseline, a spatial displacement of the Arches cluster with respect to the field population is measured to be 24.0 +/- 2.2 mas, corresponding to a proper motion of 5.6 +/- 0.5 mas/yr or 212 +/- 29 km/s at a distance of 8 kpc. In combination with the known line-of-sight velocity of the cluster, we derive a 3D space motion of 232 +/- 30 km/s of the Arches relative to the field. The large proper motion of the Arches cannot be explained with any of the closed orbital families observed in gas clouds in the bar potential of the inner Galaxy, but would be consistent with the Arches being on a transitional trajectory between x1 and x2 orbits. We investigate a cloud-cloud collision as the possible origin for the Arches cluster. The integration of the cluster orbit in the potential of the inner Galaxy suggests that the cluster passes within 10 pc of the supermassive black hole only if its true GC distance is very close to its projected distance. A contribution of young stars from the Arches cluster to the young stellar population in the inner few parsecs of the GC thus appears increasingly unlikely. The measurement of the 3D velocity and orbital analysis provides the first observational evidence that Arches-like clusters do not spiral into the GC. This confirms that no progenitor clusters to the nuclear cluster are observed at the present epoch. ------------------------------------------------------------------------ Email : matumoto@cr.scphys.kyoto-u.ac.jp Title : X-Ray Observations of the Galactic Center with Suzaku Author(s): K. Koyama, Y. Hyodo, T. Inui, M. Nobukawa and H. Mori Institute: (1) Department of Physics, Graduate School of Science, Kyoto University Paper : AN, 2008, in press EPrint : 0711.2866 Abstract: We report on the diffuse X-ray emissions from the Galactic center (GCDX) observed with the X-ray Imaging Spectrometer (XIS) on board the Suzaku satellite. The highly accurate energy calibrations and extremely low background of the XIS provide many new facts on the GCDX. These are (1) the origin of the 6.7/7.0 keV lines is collisional excitation in hot plasma, (2) new SNR and super-bubble candidates are found, (3) most of the 6.4 keV line is fluorescence by X-rays, and (4) time variability of the 6.4 keV line is found from the Sgr B2 complex. ------------------------------------------------------------------------ Email : matumoto@cr.scphys.kyoto-u.ac.jp Title : A Time-Variable X-Ray Echo: Indications of a Past Flare of the Galactic-Center Black Hole Author(s): Katsuji Koyama, Tatsuya Inui, Hironori Matsumoto, and Takeshi Go Tsuru Institute: (1) Department of Physics, Graduate school of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502 Paper : PASJ, 2008, in press EPrint : 0711.2853 Abstract: A time-variability study of the neutral iron line flux at 6.40 keV in the Sgr B2 region from data of Suzaku and Chandra is presented. The highly ionized iron line at 6.68 keV is due to Galactic Center Diffuse X-rays (GCDX), and is thus time invariable. By comparing the 6.68 keV and 6.40 keV line fluxes, we found that the 6.40 keV flux from the Sgr B2 complex region is time variable; particularly the giant molecular cloud M 0.66-0.02, known as ``Sgr B2 cloud'' is highly variable. The variability of the 6.40 keV line in intensity and spatial distribution strongly supports the scenario that the molecular clouds in the Sgr B2 region are X-ray Reflection Nebulae irradiated by the Galactic Center (GC) black hole Sgr A^*. ------------------------------------------------------------------------ (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 ========================================================================