======================================================================== G C N E W S * Newsflash * - The Newsletter for Galactic Center Research - gcnews@aoc.nrao.edu http://www.aoc.nrao.edu/~gcnews ======================================================================== Vol. 23, No. 6 Feb 16, 2006 Recently submitted papers: -------------------------- 1) Obtaining cosmic ray propagation parameters from diffuse VHE gamma-ray emission from the Galactic center ridge (Buesching et al., ApJ) 2) THERMAL SiO AND H^13CO^+ LINE OBSERVATIONS OF THE DENSE MOLECULAR CLOUD G0.11-0.11 IN THE GALACTIC CENTER REGION (Handa et al., ApJ) 3) Capture of a Red Giant by the Black Hole Sgr A* as a Possible Origin for the TeV Gamma-Rays from the Galactic Center (Lu et al., ApJ) 4) A Multi-Wavelength Study of Sgr A*: The Role of Near-IR Flares in Production of X-ray, Soft gamma-ray and Sub-millimeter Emission (Yusef-Zadeh et al., ApJ) ------------------------------------------------------------------------ Email : fskib@puk.ac.za Title : Obtaining cosmic ray propagation parameters from diffuse VHE gamma-ray emission from the Galactic center ridge Author(s): I. Buesching O.C. de Jager J. Snyman Institute: North-West University, Potchefstroom Campus, South Africa Paper : ApJ, submitted astro-ph/0602193 EPrint : astro-ph/0602193 Abstract: The recent discovery of diffuse, VHE gamma radiation from the Galactic center ridge by the H.E.S.S. telescope allow for the first time the direct determination of parameters of galactic cosmic ray propagation models. In this paper we show that the diffuse gamma radiation near the Galactic center may be explained by the interaction of VHE cosmic ray (CR) protons with the interstellar gas located in several giant molecular clouds leading to a measurement of the cosmic ray diffusion coefficient for the galactic center region of \kappa = 1.3 kpc^2Myr^-1 for a mean proton energy of 3 TeV, if we assume that the CR protons originated from a supernova event (Sgr A East), which took off about 10 kyr ago. This value of \kappa is 5 to 10 times smaller than the locally measured value. ------------------------------------------------------------------------ Email : handa@ioa.s.u-tokyo.ac.jp Title : THERMAL SiO AND H^13CO^+ LINE OBSERVATIONS OF THE DENSE MOLECULAR CLOUD G0.11-0.11 IN THE GALACTIC CENTER REGION Author(s): T. Handa M. Sakano S. Naito, M. Hiramatsu M. Tsuboi Institute: (1) Institute of Astronomy, University of Tokyo, Osawa 2-21-1, Mitaka, Tokyo 181-0011, Japan (2) Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK (3) Department of Astronomy, University of Tokyo, Hongo 7-3-1, Bunkyo, Tokyo 113-0033, Japan (4) Nobeyama Radio Observatory, National Astronomical Observatory Japan, Nobeyama, Minami-Saku, Nagano 384-1305, Japan; Department of Astronomical Science, Graduate University for Advanced Studies (Soken-Dai), Mitaka, Tokyo 181-8588, Japan; and Department of Astronomy, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan Paper : ApJ, 636, 261 EPrint : astro-ph/0510565 Abstract: We obtained the first view in H^13CO^+ J=1-0 and a high-resolution map in thermal SiO lines of G0.11-0.11, which is a molecular cloud situated between the Galactic Center radio arc and Sgr A. From a comparison with previous line observations, we found that the H^13CO^+ J=1-0 line is optically thin, whereas the thermal SiO lines are optically thick. The line intensity in H^13CO^+ J=1-0 shows that the cloud has a large column density, up to N(H_2)=(6-7)*10^23 cm^-2, which corresponds to about 640-740 mag in A_V or 10-12 mag in A_25 mu m. The estimated column density is the largest known of any even in the Galactic center region. We conclude from the intensity ratio of SiO J=1-0 to CS J=1-0 that emitting gas is highly inhomogeneous for SiO abundance on a scale smaller than the beam width 35''. ------------------------------------------------------------------------ Email : ly@bao.ac.cn Title : Capture of a Red Giant by the Black Hole Sgr A* as a Possible Origin for the TeV Gamma-Rays from the Galactic Center Author(s): Y. Lu(1,2), K. S. Cheng(2), Y. F. Huang(3,2) Institute: (1) National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China (2) Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, China (3) Department of Astronomy, Nanjing University, Nanjing 210093, China Paper : ApJ, Apr. 2006, in press Abstract: Non-thermal TeV gamma -ray emission within multi-pc scale has been observed from the center region of our galaxy. We argue that these gamma -rays are the result of a transient activity of the massive black hole Sgr A^* which resides at the Galactic center. About thousands of years ago, the black hole may have experienced an active phase by capturing a red giant star and forming an accretion disk, temporarily behaving like an active galactic nuclear. A powerful jet, which contains plenty of high speed protons, was launched during the process. These runaway protons interact with the dense ambient medium, producing TeV gamma -ray emission through the \pi^o-decay process. We show that the total energy deposited in this way is large enough to account for observations. The diffusion length of protons is also consistent with the observed size of the TeV source. ------------------------------------------------------------------------ Email : zadeh@northwestern.edu Title : A Multi-Wavelength Study of Sgr A*: The Role of Near-IR Flares in Production of X-ray, Soft gamma-ray and Sub-millimeter Emission Author(s): F. Yusef-Zadeh, H. Bushouse, C.D. Dowell, M. Wardle, D. Roberts, C. Heinke, G. C. Bower, B. Vila Vilaro, S. Shapiro, A. Goldwurm, G. Belanger Paper : ApJ (in press) EPrint : astro-ph/0510787 Abstract: Although Sgr A* is known to be variable in radio, millimeter, near-IR and X-rays, the correlation of the variability across its spectrum has not been fully studied. Here we describe highlights of the results of two observing campaigns in 2004 to investigate the correlation of flare activity in different wavelength regimes, using a total of nine ground and space-based telescopes. We report the detection of several new near-IR flares during the campaign based on HST observations. The level of near-IR flare activity can be as low as 0.15 mJy at 1.6 micron and continuous up to 40% of the total observing time, thus placing better limits than ground-based near-IR observations. Using the NICMOS instrument on the HST, the XMM-Newton and Caltech Submillimeter observatories, we also detect simultaneous bright X-ray and near-IR flare in which we observe for the first time correlated substructures as well as simultaneous submillimeter and near-IR flaring. X-ray emission is arising from the population of near-IR-synchrotron-emitting relativistic particles which scatter submillimeter seed photons within the inner 10 Schwarzschild radii (R_sch) of Sgr A* up to X-ray energies. In addition, using the inverse Compton scattering picture, we explain the high energy 20-120 keV emission from the direction toward Sgr A*, and the lack of one-to-one X-ray counterparts to near-IR flares, by the variation of the magnetic field and the spectral index distributions of this population of nonthermal particles. In this picture, the evidence for the variability of submillimeter emission during a near-IR flare is produced by the low-energy component of the population of particles emitting synchrotron near-IR emission. Based on the measurements of the duration of flares in near-IR and submillimeter wavelengths, we argue that the cooling could be due to adiabatic expansion with the implication that flare activity may drive an outflow. ------------------------------------------------------------------------ (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, Robin Herrnstein - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - For Abstract submission please follow the instructions which are at http://www.aoc.nrao.edu/~gcnews/home/submission.shtml ========================================================================