======================================================================== 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. 2 Jun 7, 2007 Recently submitted papers: -------------------------- 1) Gamma Rays from the Galactic Centre (Erlykin & Wolfendale, J.Phys) 2) Massive perturbers and the efficient merger of binary massive black holes (Perets & Alexander, eprint) 3) The Nature of Linearly Polarized Millimeter and Sub-millimeter Emission in Sagittarius A* (Liu et al., ApJ) 4) Masers as Probes of Massive Star Formation in the Nuclear Disk (Yusef-Zadeh et al., IAU242) ------------------------------------------------------------------------ Email : erlykin@migmail.ru Title : Gamma Rays from the Galactic Centre Author(s): A.D.Erlykin ^1,2, A.W.Wolfendale ^2 Institute: (1) P. N. Lebedev Physical Institute, Moscow, Russia (2) Department of Physics, University of Durham, Durham, UK Paper : J.Phys,G: Nucl.Part.Phys. EPrint : arXiv:0705.2333 Abstract: Recent results from the HESS gamma ray telescope have shown the presence of both a diffuse, extended, flux of gamma rays above 0.4 TeV and discrete sources in and near the Galactic Centre. Here, we put forward a possible explanation in terms of the diffusion of cosmic ray protons from a succession of supernova remnants ( SNR ) in the SgrA* region of the Galaxy plus a contribution from SNR in the rest of the Galactic Centre Region, to be called the Galactic Centre Ridge ( GCR ). Protons are favoured over electrons because the mG magnetic fields in the Region will attenuate energetic electrons = severely. Prominent features are the need for 'anomalous diffusion' of the protons in the whole region and the adoption of low efficiency for SNR acceleration in the high density regions. The latter is related by us to the well-known low 'cosmic ray gradient' in the Galaxy. A corroborating feature is the close correlation of inferred cosmic ray intensity with the smoothed intensity of 5 GHz radio radiation. We attribute this to the presence of the SNR in the GCR. ------------------------------------------------------------------------ Email : hagai.perets@weizmann.ac.il Title : Massive perturbers and the efficient merger of binary massive black holes Author(s): Hagai Perets, Tal Alexander(1) Institute: Faculty of Physics, Weizmann Institute of Science, POB 26, Rehovot 76100, Israel (1) The William Z. & Eda Bess Novick career development chair Paper : eprint EPrint : arXiv:0705.2123 Abstract: We show that dynamical relaxation in the aftermath of a galactic merger, and the ensuing formation of a binary massive black hole (MBH), are dominated by massive perturbers (MPs), such as giant molecular clouds or clusters. MPs accelerate relaxation by orders of magnitude relative to 2-body stellar relaxation alone, and efficiently scatter stars into the binary MBH's orbit. The 3-body star-binary MBH interactions shrink the binary MBH to the point where energy loss from the emission of gravitational waves (GW) leads to rapid coalescence. We take into account the decreased efficiency of the star-binary MBH interaction due to acceleration in the galactic potential, and show that the observed MP abundances in galactic nuclei imply binary MBH coalescence times shorter than the Hubble time. These events are observable by their strong GW emission. MPs thus increase the cosmic rate of these GW events, increase the mass deficit in the stellar core, lead to the ejection of hyper-velocity stars, and suppress the formation of triple MBH systems and the resulting ejection of MBHs into intergalactic space. ------------------------------------------------------------------------ Email : qianl@vega.bac.pku.edu.cn Title : The Nature of Linearly Polarized Millimeter and Sub-millimeter Emission in Sagittarius A* Author(s): Siming Liu(1), Lei Qian(2), Xue-Bing Wu(2), Christopher L. Fryer(1,3) and Hui Li(1) Institute: (1) Los Alamos National Laboratory, Los Alamos, NM 87545 (2) Department of Astronomy, Peking University, Beijing 100871 (3) Physics Department, The University of Arizona, Tucson, AZ 85721 Paper : ApJ, May 2005, submitted Abstract: The linearly polarized millimeter and sub-millimeter emission in Sagittarius A* is produced within 10 Schwarzschild radii of the supermassive black hole at the Galactic Center. We show that the millimeter emission likely originates from a hot accretion disk, where electrons are heated efficiently by turbulent plasma waves. The observed flux density and polarization requires that the disk have an inclination angle of 45^o and its rotation axis be aligned with the major axis of the intrinsic polarization. The disk also needs to be strongly magnetized with a magnetic field energy density comparable to the thermal energy density of the gas. The high flux density and hard spectrum of the sub-millimeter (<1 mm) emission, on the other hand, suggest that it is emitted from small emission regions and therefore associated with flare events occurring either in coronas of the disk or within the last stable orbit. Simultaneous spectrum and polarization measurements will be able to test the model. ------------------------------------------------------------------------ Email : zadeh@northwestern.edu Title : Masers as Probes of Massive Star Formation in the Nuclear Disk Author(s): F. Yusef-Zadeh, R. G. Arendt, C. O. Heinke, J. L. Hinz, J. W. Hewitt, P. Pratap, S. V. Ramirez, G. H. Rieke, D. A. Roberts, S. R. Stolovy, M. Wardle, B. A. Whitney Paper : IAU242, submitted EPrint : arXiv:0705.3001 Abstract: OH(1720 MHz) and methanol masers are now recognized to be excellent probes of the interactions of supernova remnants with molecular clouds and tracers of massive star formation, respectively. To better understand the nature of star formation activity in the central region of the Galaxy, we have used these two classes of masers combined with the IRAC and MIPS data to study prominent sites of ongoing star formation in the nuclear disk. The nuclear disk is characterized by massive GMCs with elevated gas temperatures, compared to their dust temperatures. We note an association between methanol masers and a class of mid-infrared ``green sources''. These highly embedded YSOs show enhanced 4.5micron emission due to excited molecular lines. The distribution of methanol masers and supernova remnants suggest a low efficiency of star formation (with the exception of Sgr B2), which we believe is due to an enhanced flux of cosmic ray electrons impacting molecular clouds in the nuclear disk. We also highlight the importance of cosmic rays in their ability to heat molecular clouds, and thus increase the gas temperature. ------------------------------------------------------------------------ (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 ========================================================================