======================================================================== G C N E W S * Newsflash * - The Newsletter for Galactic Center Research - gcnews@aoc.nrao.edu http://www.aoc.nrao.edu/~gcnews ======================================================================== Vol. 16, No. 5 Sep 26, 2003 Recently submitted papers: -------------------------- 1) Variable Infrared Emission from the Supermassive Black Hole at the Center of the Milky Way (Ghez et al., submitted) ------------------------------------------------------------------------ Email : ghez@astro.ucla.edu Title : Variable Infrared Emission from the Supermassive Black Hole at the Center of the Milky Way Author(s): A. M. Ghez, S. A. Wright K. Matthews, D. Thompson, D. Le Mignant, M. Morris, A. Tanner, S. D. Hornstein, E. E. Becklin, B. T. Soifer Institute: (1) UCLA Department of Physics and Astronomy, Los Angeles, CA 90095 -1562; ghez, saw, morris, tanner, seth, becklin@astro.ucla.edu, (2) Caltech Optical Observatories, California Institute of Technology, MS 320-47, Pasadena, CA 91125; kym, djt, bts@irastro.caltech.edu, (3) W. M. Keck Observatory, 65-1120 Mamalahoa Hwy, Kamuela, HI 96743; davidl@keck.hawaii.edu Paper : submitted EPrint : astro-ph/0309076 Web : http://www.astro.ucla.edu/research/galcenter/ Abstract: We report the detection of a variable point source, imaged at L'(3.8 microns) with the W. M. Keck II 10-meter telescope's adaptive optics system, that is coincident to within 12 mas of the Galaxy's central supermassive black hole and the unique radio source Sgr A*. While in 2002 this source (SgrA*-IR) was confused with the stellar source S0-2, in 2003 these two sources are separated by 87 mas allowing the new source's properties to be determined directly. On four separate nights, its observed L' magnitude ranges from 12.2 to 13.8, which corresponds to a flux density of 0.7 - 3 mJy, observed, and 4 - 17 mJy, dereddened; no other source in this region shows such large variations in flux density - a factor of 4 over a week and a factor of 2 over 40 min. In addition, it has a K-L' color greater than 2.1, which is at least 1 mag redder than any other source detected at L' in its vicinity. Between 2002 and 2003, the new source has no significant proper motion with an upper limit of 300 km/s, which is a factor of >20 smaller than that of the stellar sources measured within 10 mas of the dynamical center. Based on this source's coincidence with the Galaxy's dynamical center, its lack of motion, its variability, and its red color, we conclude that it is associated with the central supermassive black hole. The short timescale for the 3.8 micron flux density variations implies that the emission arises in the accretion flow on physical size scales smaller than 5 AU, or 80 R_s for a 4x10^6 Mo black hole. We suggest that the 3.8 micron emission mechanism is synchrotron emission from the same population of electrons that gives rise to the X-ray flares, which implies that processes that can give rise to a high-energy power-law tail in the electron energy distribution are much more common than previously thought. ------------------------------------------------------------------------ (Older versions of the Newsflash can be found at the gcnews web-page) ======================================================================== Edited by Angela Cotera Sera Markoff Lorant Sjouwerman (cotera@asu.edu) (sera@space.mit.edu) (lsjouwerman@aoc.nrao.edu) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - For Abstract submission please follow the instructions which are at http://www.aoc.nrao.edu/~gcnews/home/submission.shtml ========================================================================