======================================================================== 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. 8 Nov 16, 2006 Recently submitted papers: -------------------------- 1) Galactic Centre X-ray Sources (Gosling et al., AIP Conf) 2) The Nature of the Variable Galactic Center Source GCIRS 16SW Revisited: A Massive Eclipsing Binary (Peeples et al., ApJL) 3) The Origin of Diffuse X-ray and gamma -ray Emission from the Galactic Center Region: Cosmic Ray Particles (Yusef-Zadeh et al, ApJ) ------------------------------------------------------------------------ Email : ajgosling@gmail.com Title : Galactic Centre X-ray Sources Author(s): A. J. Gosling R. M. Bandyopadhyay K. M. Blundell Paper : Poster to appear in AIP Conf. Proc.: `The Multicoloured Landscape of Compact Objects and their Explosive Origins'; Cefalu, Sicily, 2006 June 11-24 EPrint : astro-ph/0611177 Abstract: We report on a campaign to identify the counterparts to the population of X-ray sources discovered at the centre of our Galaxy by Wang et al. (2002) using Chandra. We have used deep, near infrared images obtained on VLT/ISAAC to identify candidate counterparts as astrometric matches to the X-ray positions. Follow up Ks-band spectroscopic observations of the candidate counterparts are used to search for accretions signatures in the spectrum, namely the Brackett- gamma emission line (Bandyopadhyay et al.1997). From our small initial sample, it appears that only a small percentage, 2 - 3 % of the 1000 X-ray sources are high mass X-ray binaries or wind accreting neutron stars, and that the vast majority will be shown to be canonical low mass X-ray binaries and cataclysmic variables. ------------------------------------------------------------------------ Email : molly@astronomy.ohio-state.edu Title : The Nature of the Variable Galactic Center Source GCIRS 16SW Revisited: A Massive Eclipsing Binary Author(s): Molly S. Peeples (1), A. Z. Bonanos (2), D. L. DePoy (1), K. Z. Stanek (1), J. Pepper (1), Richard W. Pogge (1), M. H. Pinsonneault (1), K. Sellgren (1) Institute: (1) Ohio State (2) Carnegie Institute of Washington Paper : ApJL, accepted EPrint : astro-ph/0610212 Abstract: We present a re-analysis of our H- and K-band photometry and light-curves for GCIRS 16SW, a regular periodic source near the Galactic center. These data include those presented by DePoy et al. (2004); we correct a sign error in their reduction, finding GCIRS 16SW to be an eclipsing binary with no color variations. We find the system to be an equal mass overcontact binary (both stars overfilling their Roche lobes) in a circular orbit with a period P=19.4513 days, an inclination angle i=71 degrees. This confirms and strengthens the findings of Martins et al. (2006) that GCIRS 16SW is an eclipsing binary composed of two 50Msun stars, further supporting evidence of recent star formation very close to the Galactic center. Finally, the calculated luminosity of each component is close to the Eddington luminosity, implying that the temperature of 24400 K given by Najarro et al. (1997) might be overestimated for these evolved stars. ------------------------------------------------------------------------ Email : zadeh@northwestern.edu Title : The Origin of Diffuse X-ray and gamma -ray Emission from the Galactic Center Region: Cosmic Ray Particles Author(s): F. Yusef-Zadeh(1), M. Muno(2), M. Wardle(3), D.C. Lis(4) Institute: (1) Department of Physics and Astronomy, Northwestern University, Evanston, Il. 60208 (2) Dept Physics and Astronomy, University of California, Los Angeles, Box 951547, Los Angeles, CA 90095 (3) Department of Physics, Macquarie University, Sydney NSW 2109, Australia (4) California Institute of Technology, MC 320-47, Pasadena, CA 91125 Paper : ApJ, Feb 2007, in press Abstract: The inner couple hundred pcs of our Galaxy is characterized by significant amount of synchrotron-emitting gas, which appears to co-exist with a large reservoir of molecular gas. Many of the best studied sources in this region exhibit a mixture of 6.4 keV Fe K alpha emission, molecular line emission and nonthermal radio continuum radiation. The spatial correlation between  fluorescent Fe K- alpha line  emission at 6.4 keV and molecular line emission  from Galactic center molecular clouds has been explained as reflected X-rays from a past outburst of Sgr A*. Here we present multi-wavelength study of a representative Galactic center cloud Sgr C using Chandra, VLA and FCRAO. We note a correlation between the nonthermal radio filaments in Sgr C and the X-ray features, suggesting that the two are related. This correlation, when combined with the distribution of molecular gas suggests against the irradiation of Sgr C by Sgr A*. Instead, we account for this distribution in terms of the impact of the relativistic particles from local (nonthermal filaments) and extended sources with diffuse neutral gas producing both a nonthermal bremsstrahlung X-ray continuum emission, as well as diffuse 6.4 keV line emission. The production rate of Fe K alpha photons associated with the injection of electrons into a cloud as a function of column density is calculated. The required energy density of low-energy cosmic rays associated with the synchrotron emitting radio filaments or extended features is estimated to be in the range between 20 and 10^3 eV cm^-3 for Sgr C, Sgr B1, Sgr B2, and ``the 45 and -30 km s^-1'' clouds. We also generalize this idea to explain the cosmic-ray heating of molecular gas, the interstellar cosmic ray ionization, the pervasive production of diffuse K alpha line and TeV emission from the Galactic center molecular clouds. In particular, we suggest that Inverse Compton scattering of the sub-millimeter radiation from dust by relativistic electrons may contribute substantially to the large-scale diffuse TeV emission observed towards the central regions of the Galaxy. ------------------------------------------------------------------------ (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 ========================================================================