======================================================================== G C N E W S * Newsflash * - The Newsletter for Galactic Center Research - gcnews@aoc.nrao.edu http://www.aoc.nrao.edu/~gcnews ======================================================================== Vol. 26, No. 2 Jan 25, 2007 Recently submitted papers: -------------------------- 1) Far-Infrared detection of H_2D^+ toward SgrB2 (Cernicharo et al., ApJ) 2) Photometric Stellar Variability in the Galactic Center (Rafelski et al., ApJ) 3) A Faint, Steep Spectrum Burst from the Radio Transient GCRT J1745-3009 (Hyman et al., ApJLetters) ------------------------------------------------------------------------ Email : javier.rodriguez-goicoechea@lra.ens.fr Title : Far-Infrared detection of H_2D^+ toward SgrB2 Author(s): J. Cernicharo, E. Polehampton, J.R. Goicoechea Institute: (1)Departamento de Astrofisica Molecular e Infrarroja, Instituto de Estructura de la Materia, CSIC, C/ Serrano 121, 28006, Madrid, Spain, (2) Space Science \& Technology Department, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11 0QX, UK, (3) LERMA-LRA, UMR 811, CNRS, Observatoire de Paris et Ecole Normale Superieure, 24 rue Lhomond, 75231 Paris Cedex 05, France, Paper : ApJ letters, 2007, in press EPrint : astro-ph/0701559 Abstract: We repport on the first far-IR detection of H_2D^+, using the Infrared Space Observatory, in the line of sight toward Sgr B2 in the galactic center. The transition connecting the ground level of o-H_2D^+, 1_1,1, with the the 2_1,2 level at 113 K is observed in absorption against the continuum emission of the cold dust of the source. The line is broad, with a total absorption covering 350 km s^-1, i.e., similar to that observed in the fundamental transitions of H_2O, OH and CH at 179, 119 and 149 micron respectively. For the physical conditions of the different absorbing clouds the H_2D^+ column density ranges from 2 to 5*10^13 cm^-2, i.e., near an order of magnitude below the upper limits obtained from ground based submillimeter telescopes. The derived H_2D^+ abundance is of a few 10^-10, which agrees with chemical models predictions for a gas at a kinetic temperature of 20 K. ------------------------------------------------------------------------ Email : marcar@ucla.edu Title : Photometric Stellar Variability in the Galactic Center Author(s): M. Rafelski, A. M. Ghez, S. D. Hornstein, J. R. Lu, M. Morris Institute: (1) Division of Astronomy and Astrophysics, UCLA, Los Angeles, CA 90095-1547 Paper : ApJ, April 2007, in press EPrint : astro-ph/0701082 Abstract: We report the results of a diffraction-limited, photometric variability study of the central 5\tt'' * 5\tt'' of the Galaxy conducted over the past 10 years using speckle imaging techniques on the W. M. Keck I 10 m telescope. Within our limiting magnitude of m_K < 16 mag for images made from a single night of data, we find a minimum of 15 K[2.2 micron ]-band variable stars out of 131 monitored stars. While large populations of binaries have been posited to exist in this region, both to explain the presence of young stars in the vicinity of a black hole and because of the high stellar densities, only two binaries are identified in this study. First is the previously identified Ofpe/WN9 equal mass eclipsing binary star IRS 16SW, for which we measure an orbital period of 19.448 +/- 0.002 days. In contrast to recent results, our data on IRS 16SW show an asymmetric phased light curve with a much steeper fall-time than rise-time, which may be due to tidal deformations caused by the proximity of the stars in their orbits. Second is the WC 9 Wolf-Rayet star IRS 29N; its observed photometric variation over a few year time-scale is likely due to episodic dust production in a binary system containing two windy stars. Our sample also includes 4 candidate Luminous Blue Variable (LBV) stars (IRS 16NE, 16C, 16NW, 16SW). While 2 of them show variability, none show the characteristic of LBVs large increase or decrease in luminosity. However, our time baseline is too short to rule them out as LBVs. Nonetheless, the lack of evidence for these stars to be LBVs and their coexistence with a significant surrounding population of well established Wolf-Rayet stars is consistent with needing only a single recent starburst event at the Galactic center to account for all of the known, young, massive stars. Among the remaining variable stars, the majority are early-type stars and three are possibly variable due to line of sight extinction variations. For the 7 OB stars at the center of our field of view that have well- determined 3-dimensional orbits, we see no evidence of flares or dimming of their light, which limits the possibility of a cold, geometrically-thin inactive accretion disk around the supermassive black hole, Sgr A^*. ------------------------------------------------------------------------ Email : shyman@sbc.edu Title : A Faint, Steep Spectrum Burst from the Radio Transient GCRT J1745-3009 Author(s): Scott D. Hyman Subhashis Roy Sabyasachi Pal T. Joseph W. Lazio Paul S. Ray Namir E. Kassim S. Bhatnagar Institute: (1) Department of Physics and Engineering, Sweet Briar College, Sweet Briar, VA 24595 (2) ASTRON, P.O. Box 2, 7990 AA Dwingeloo, The Netherlands. (3) National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune, India (4) Remote Sensing Division, Naval Research Laboratory, Washington, DC 20375-5351 (5) E. O. Hulburt Center for Space Research, Naval Research Laboratory, Washington, DC 20375-5352 (6) Remote Sensing Division, Naval Research Laboratory, Washington, DC 20375-5351 (7) National Radio Astronomy Observatory, Array Operations Center, P.O. Box O, 1003 Lopezville Road, Socorro, NM 87801-0387 Paper : ApJLetters, submitted EPrint : astro-ph/0701098 Abstract: GCRT J1745-3009 is a transient bursting radio source located in the direction of the Galactic center. It was discovered in a 330 MHz VLA observation from 2002 September 30-October 1 and subsequently rediscovered in a 330 MHz GMRT observation from 2003 September 28 by Hyman et al. Here we report a new radio detection of the source in 330 MHz GMRT data taken on 2004 March 20. The observed properties of the single burst detected differ significantly from those measured previously, suggesting that GCRT J1745-3009 was detected in a new physical state. The 2004 flux density was 0.05 Jy, 10* weaker than the single 2003 burst and 30* weaker than the five bursts detected in 2002. We derive a very steep spectral index, alpha = -13.5 +/- 3.0, across the bandpass, a new result previously not detectable due to limitations in the analysis of the 2002 and 2003 observations. Also, the burst was detected for only 2 min., in contrast to the 10 min. duration observed in the earlier bursts. Due to sparse sampling, only the single burst was detected in 2004, as in the 2003 epoch, and we cannot rule out additional undetected bursts that may have occurred with the same 77 min. periodicity observed in 2002 or with a different periodicity. Considering our total time on source throughout both our archival and active monitoring campaigns, we estimate the source exhibits detectable bursting activity 7% of the time. ------------------------------------------------------------------------ (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 ========================================================================