======================================================================== G C N E W S * Newsflash * - The Newsletter for Galactic Center Research - gcnews@aoc.nrao.edu http://www.aoc.nrao.edu/~gcnews ======================================================================== Vol. 25, No. 1 Jul 28, 2006 Recently submitted papers: -------------------------- 1) Inverse Compton Scenarios for the TeV Gamma-Ray Emission of the Galactic Centre (Hinton & Aharonian, ApJ) 2) A RIAF Interpretation for the Past Higher Activity of the Galactic Center Black Hole and the 511 keV Annihilation Emission (TOTANI, PASJ.) ------------------------------------------------------------------------ Email : hinton@mpimail.mpi-hd.mpg.de Title : Inverse Compton Scenarios for the TeV Gamma-Ray Emission of the Galactic Centre Author(s): J. A. Hinton F. A. Aharonian Institute: (1) Max-Planck-Institut fuer Kernphysik, P.O. Box 103980, D 69029 Heidelberg, Germany (2) Landessternwarte, Universitaet Heidelberg, Koenigstuhl, D 69117 Heidelberg, Germany (3) Max-Planck-Institut fuer Kernphysik, P.O. Box 103980, D 69029 Heidelberg, Germany Paper : ApJ submitted EPrint : astro-ph/0607557 Abstract: The intense Compton cooling of ultra-relativistic electrons in the Klein-Nishina regime in radiation dominated environments, such as that found in the Galactic Centre, may result in radically different electron spectra than those produced by Synchrotron cooling. We explore these effects and their impact on the X-ray and gamma -ray spectra produced in electron accelerators in this region in comparison to elsewhere in our galaxy. We discuss the broad-band emission expected from the newly discovered pulsar wind nebula G 359.95-0.04 and the possible relationship of this X-ray source to the central TeV gamma -ray source HESS J1745-290. Finally we discuss the possible relationship of the Galactic Centre INTEGRAL source IGR J1745.6-2901 to the TeV emission. ------------------------------------------------------------------------ Email : totani@kusastro.kyoto-u.ac.jp Title : A RIAF Interpretation for the Past Higher Activity of the Galactic Center Black Hole and the 511 keV Annihilation Emission Author(s): Tomonori TOTANI Institute: (1) Department of Astronomy, Kyoto University, Sakyo-ku, Kyoto 606-8502 Paper : PASJ. July 2006. submitted EPrint : astro-ph/0607414 Abstract: There are several lines of evidence that the super-massive black hole at the Galactic center had higher activities in the past than directly observed at present. Here I show that these lines of evidence can quantitatively and consistently be explained if the mean accretion rate during the past 10^7 yrs has been 10^3-4 times higher than the current rate, by the picture of radiatively inefficient accretion flow (RIAF) and associated outflow that has been successfully applied to Sgr A^*. I argue that this increased rate and its duration are theoretically reasonable in the Galactic center environment, while the accretion rate suddenly dropped about 300 years ago most likely because of the shell passage of the supernova remnant Sgr A East. Then I show that a significant amount of positrons should have been created around the event horizon during the higher activity phase, and injected into interstellar medium by the outflow. The predicted positron production rate and propagation distance are close to those required to explain the observed 511 keV annihilation line emission from the Galactic bulge, giving a natural explanation for the large bulge-to-disk ratio of the emission. The expected injection energy is MeV, which is also favorable as an explanation of the 511 keV line emission. ------------------------------------------------------------------------ (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 ========================================================================