======================================================================== 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. 13 Jan 8, 2008 Recently submitted papers: -------------------------- 1) An X-ray, IR, and Submillimeter Flare of Sagittarius A* (Marrone et al., ApJ) 2) Infall and Outflow of Molecular Gas in Sgr B2 (Qin et al., ApJ) 3) Simultaneous Chandra, CSO and VLA Observations of Sgr A*: The Nature of Flaring Activity (Yusef-Zadeh et al., ApJ) ------------------------------------------------------------------------ Email : dmarrone@oddjob.uchicago.edu Title : An X-ray, IR, and Submillimeter Flare of Sagittarius A* Author(s): D. P. Marrone(1,2), F. K. Baganoff(3), M. Morris(4), J. M. Moran(5), A. M. Ghez(4,6), S. D. Hornstein(7), C. D. Dowell(8), D. J. Munoz(5), M. W. Bautz(3), G. R. Ricker(3), W. N. Brandt(9), G. P. Garmire(9), J. R. Lu(4), K. Matthews(10), J.-H. Zhao(5), R. Rao(11), and G. C. Bower(12) Institute: (1) Jansky Postdoctoral Fellow, National Radio Astronomy Observatory (2) Kavli Institute for Cosmological Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL, 60637 (3) Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139-4307 (4) Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547 (5) Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (6) Institute for Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095-1565 (7) Center for Astrophysics and Space Astronomy, Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309 (8) Department of Physics, California Institute of Technology, Pasadena, CA 91125 (9) Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802-6305 (10) Caltech Optical Observatories, California Institute of Technology, MS 320-47, Pasadena, CA 91125 (11) Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 10617, Taiwan (12) Department of Astronomy and Radio Astronomy Laboratory, University of California at Berkeley, Campbell Hall, Berkeley, CA 94720 Paper : ApJ, submitted EPrint : 0712.2877 Abstract: Energetic flares are observed in the Galactic supermassive black hole Sagittarius A* from radio to X-ray wavelengths. On a few occasions, simultaneous flares have been detected in IR and X-ray observations, but clear counterparts at longer wavelengths have not been seen. We present a flare observed over several hours on July 17, 2006 with the Chandra X-ray Observatory, the Keck II telescope, the Caltech Submillimeter Observatory, and the Submillimeter Array. All telescopes observed strong flare events, but the submillimeter peak is found to occur nearly 100 minutes after the X-ray peak. Submillimeter polarization data show a polarization signature in the excess flare emission, increasing from 9% to 17% fractional polarization as the flare passes through its peak, consistent with a transition from optically thick to thin synchrotron emission. The temporal and spectral behavior of the flare requires that the energetic electrons responsible for the emission cool faster than expected from their radiative output. This is consistent with adiabatic cooling in an expanding emission region, with X-rays produced through self-Compton scattering. We also present the submillimeter detection of an IR flare on July 31, 2005, which showed a larger peak IR flux and similar submillimeter flux but did not have measurable X-ray emission. This flare also shows a delay between the IR peak and submillimeter peak, although it is significantly shorter. The submillimeter lag and the variable ratio of IR and X-ray luminosities are related through a synchrotron and self-Compton model. ------------------------------------------------------------------------ Email : slqin@bao.ac.cn Title : Infall and Outflow of Molecular Gas in Sgr B2 Author(s): Sheng-Li Qin(1,2), Jun-Hui Zhao(1), James M. Moran(1), Daniel P. Marrone(1), Nimesh A. Patel(1), Jun-Jie Wang(2), Sheng-Yuan Liu(3), Yi-Jehng Kuan(3,4) Institute: (1) Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 42, Cambridge, MA 02138; sqin@cfa.harvard.edu. (2) National Astronomical Observatories, Chinese Academy of Sciences, Beijing, 100012. (3) Academia Sinica Institute of Astronomy and Astrophysics, P.O.Box 23-141, Taipei 106, Taiwan. (4) Department of Earth Sciences, National Taiwan Normal University, 88 Section 4, Ting-Chou Road, Taipei 116, Taiwan. Paper : ApJ, acceptedd EPrint : 0801.0348 Abstract: bservations of two H_2CO (3_03-2_02 and 3_21-2_20) lines and continuum emission at 1.3 mm towards Sgr B2(N) and Sgr B2(M) have been carried out with the SMA. The mosaic maps of Sgr B2(N) and Sgr B2(M) in both continuum and lines show a complex distribution of dust and molecular gas in both clumps and filaments surrounding the compact star formation cores. We have observed a decelerating outflow originated from the Sgr B2(M) core, showing that both the red-shifted and blue-shifted outflow components have a common terminal velocity. This terminal velocity is 58+/-2 km s^-1. It provides an excellent method in determination of the systematic velocity of the molecular cloud. The SMA observations have also shown that a large fraction of absorption against the two continuum cores is red-shifted with respect to the systematic velocities of Sgr B2(N) and Sgr B2(M), respectively, suggesting that the majority of the dense molecular gas is flowing into the two major cores where massive stars have been formed. We have solved the radiative transfer in a multi-level system with LVG approximation. The observed H_2CO line intensities and their ratios can be adequately fitted with this model for the most of the gas components. However, the line intensities between the higher energy level transition H_2CO (3_21-2_20) and the lower energy level transition H_2CO (3_03-2_02) is reversed in the red-shifted outflow region of Sgr B2(M), suggesting the presence of inversion in population between the ground levels in the two K ladders (K_-1= 0 and 2). The possibility of weak maser processes for the H_2CO emission in Sgr B2(M) is discussed. ------------------------------------------------------------------------ Email : zadeh@northwestern.edu Title : Simultaneous Chandra, CSO and VLA Observations of Sgr A*: The Nature of Flaring Activity Author(s): Yusef-Zadeh, F., Wardle, M.; Heinke, C.; Dowell, C. D.; Roberts, D., Baganoff, F. K. and Bower, G. C. Paper : ApJ, submitted EPrint : 0712.2882 Abstract: Sgr A*, the massive black hole at the center of the Galaxy, varies in radio through X-ray emission on hourly time scales. The flare activity is thought to arise from the innermost region of an accretion flow onto Sgr A*. We present simultaneous light curves of Sgr A* in radio, sub-mm and X-rays that show a possible time delay of 110+/-17 minutes between X-ray and 850 micron suggesting that the sub-mm flare emission is optically thick. At radio wavelengths, we detect time lags of of 20.4+/-6.8, 30+/-12 and 20+/-6 minutes between the flare peaks observed at 13 and 7 mm in three different epochs using the VLA. Linear polarization of 1+/-0.2% and 0.7+/-0.1% is detected at 7 and 13 mm, respectively, when averaged over the entire observation on 2006 July 17. A simple picture of an expanding bubble of synchrotron emitting hot plasma can explain the time delay between various wavelengths, the asymmetric shape of the light curves, and the observed polarization of the flare emission at 43 and 22 GHz. The derived physical quantities that characterize the flare emission give the blob expansion speed of v_exp 0.003-0.1c, magnetic field of B 10-70 Gauss and particle spectral index p 1-2. These parameters suggest that the expanding gas can not escape from Sgr A* unless it has a large bulk motion. ------------------------------------------------------------------------ (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 ========================================================================