======================================================================== 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. 10 Dec 15, 2006 Recently submitted papers: -------------------------- 1) Gravitational wave bursts from the Galactic massive black hole (Hopman & Larson, astro-ph/0612337) 2) Determining the nature of the faint X-ray source population near the Galactic Centre (Bandyopadhyay et al., PoS) 3) The Position of Sagittarius A*: III. Motion of the Stellar Cusp (Reid et al., ApJ) ------------------------------------------------------------------------ Email : clovis@strw.leidenuniv.nl Title : Gravitational wave bursts from the Galactic massive black hole Author(s): Clovis Hopman^1, Marc Freitag^2 and Shane L. Larson^3 Institute: ^1Leiden University, Leiden Observatory, P.O. Box 9513, NL-2300 RA Leiden ^2 Institute of Astronomy, University of Cambridge, Madingley Road, CB3 0HA Cambridge, UK ^3Department of Physics, Weber State University, Ogden, UT 84408 Paper : astro-ph/0612337 (submitted to MNRAS) EPrint : astro-ph/0612337 Abstract: The Galactic massive black hole (MBH), with a mass of Mbh=3.6*10^6 Mo, is the closest known MBH, at a distance of only 8 kpc. The proximity of this MBH makes it possible to observe gravitational waves from stars with periapse in the observational frequency window of the Laser Interferometer Space Antenna (LISA). This is possible even if the orbit of the star is very eccentric, so that the orbital frequency is many orders of magnitude below the LISA frequency window, as suggested by Rubbo et al. (2006). Here we give an analytical estimate of the detection rate of such gravitational wave bursts. The burst rate is critically sensitive to the inner cut-off of the stellar density profile. Our model accounts for mass-segregation and for the physics determining the inner radius of the cusp, such as stellar collisions, energy dissipation by gravitational wave emission, and consequences of the finite number of stars. We find that stellar black holes have a burst rate of the order of 1/yr, while the rate is of order <0.1/yr for main sequence stars and white dwarfs. These analytical estimates are supported by a series of Monte Carlo samplings of the expected distribution of stars around the Galactic MBH, which yield the full probability distribution for the rates. We estimate that no burst will be observable from the Virgo cluster. ------------------------------------------------------------------------ Email : reba@astro.ufl.edu Title : Determining the nature of the faint X-ray source population near the Galactic Centre Author(s): Reba M. Bandyopadhyay(1), Andrew J. Gosling, Katherine M. Blundell, Philipp Podsiadlowski(2), Stephen E. Eikenberry, Valerie J. Mikles(3), James C.A. Miller-Jones(4), Franz E. Bauer(5) Institute: 1) Dept. of Astronomy, University of Florida, Gainesville, FL 32611 USA 2) Dept. of Astrophysics, University of Oxford, Oxford OX1 3RH, UK 3) Dept. of Astronomy, University of Florida, Gainesville, FL 32611 USA 4) Astronomical Institute ``Anton Pannekoek'', University of Amsterdam, NL 5) Columbia University, New York, NY 10027, USA Paper : PoS, 2006 EPrint : astro-ph/0612007 Web : http://www.astro.ufl.edu/~reba/mqw_rmb.pdf Abstract: We present results of a multi-wavelength program to study the faint discrete X-ray source population discovered by Chandra in the Galactic Centre (GC). From IR imaging obtained with the VLT we identify candidate K-band counterparts to 75% of the X-ray sources in our sample. By combining follow-up VLT K-band spectroscopy of a subset of these candidate counterparts with the magnitude limits of our photometric survey, we suggest that only a small percentage of the sources are HMXBs, while the majority are likely to be canonical LMXBs and CVs at the distance of the GC. In addition, we present our discovery of highly structured small-scale (5-15'') extinction towards the Galactic Centre. This is the finest-scale extinction study of the Galactic Centre to date. Finally, from these VLT observations we are able to place constraints on the stellar counterpart to the ``bursting pulsar'' GRO J1744-28. ------------------------------------------------------------------------ Email : reid@cfa.harvard.edu Title : The Position of Sagittarius A*: III. Motion of the Stellar Cusp Author(s): M. J. Reid, K. M. Menten, S. Trippe, T. Ott \& R. Genzel Institute: (1) Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (2) Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, D-53121 Bonn, Germany (3) Max-Planck-Institut fuer extraterrestrische Physik, Postfach 1312, D-85741 Garching, Germany Paper : ApJ, 2007, accepted EPrint : astro-ph/0612164 Abstract: In the first two papers of this series, we determined the position of Sgr A* on infrared images, by aligning the positions of red giant stars with positions measured at radio wavelengths for their circumstellar SiO masers. In this paper, we report detections of 5 new stellar SiO masers within 50'' (2 pc) of Sgr A* and new and/or improved positions and proper motions of 15 stellar SiO masers. The current accuracies are 1 mas in position and 0.3 mas/yr in proper motion. We find that the proper motion of the central stellar cluster with respect to Sgr A* is less than 45 km/s. One star, IRS 9, has a three-dimensional speed of 370 km/s at a projected distance of 0.33 pc from Sgr A*. If IRS 9 is bound to the inner parsec, this requires an enclosed mass that exceeds current estimates of the sum of the mass of Sgr A* and luminous stars in the stellar cusp by 0.8*10^6 Msun. Possible explanations include i) that IRS 9 is not bound to the central parsec and has ``fallen'' from a radius greater than 9 pc, ii) that a cluster of dark stellar remnants accounts for some of the excess mass, and/or iii) that R_0 is considerably greater than 8 kpc. ------------------------------------------------------------------------ (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 ========================================================================