======================================================================== G C N E W S * Newsflash * - The Newsletter for Galactic Center Research - gcnews@aoc.nrao.edu http://www.aoc.nrao.edu/~gcnews ======================================================================== Vol. 22, No. 3 Sep 1, 2005 Recently submitted papers: -------------------------- 1) Repeated X-ray Flaring Activity in Sagittarius A* (Belanger et al., ApJ) 2) A Persistent High-energy Flux from the Heart of the Milky Way: Integral's view of the Galactic Center (Belanger et al., ApJ) 3) CH 3 GHz Observations of the Galactic Center (Magnani et al., ApJ) 4) A New Radio Detection of the Bursting Source GCRT J1745-3009 (Hyman et al., ApJ) ------------------------------------------------------------------------ Email : belanger@cea.fr Title : Repeated X-ray Flaring Activity in Sagittarius A* Author(s): G. Belanger(1,2), A. Goldwurm,(1,2), F. Melia(3), P. Ferrando,(1,2), N. Grosso(4), D. Porquet(5), R. Warwick(6), F. Yusef-Zadeh(7) Institute: (1) Service d'Astrophysique, DAPNIA/DSM/CEA, 91191 Gif-sur-Yvette, France (2) Unite mixte de recherche Astroparticule et Cosmologie, 11 place Berthelot, 75005 Paris, France (3) Department of Physics and Steward Observatory, University of Arizona, Tucson, AZ 85721, USA (4) Laboratoire d'Astrophysique de Grenoble, Universite Joseph-Fourier, 38041 Grenoble, France (5) Max-Planck-Institute fuer extraterrestrische Physik, Munich D-85741, Germany (6) Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK (7) Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208 Paper : ApJ, accepted EPrint : astro-ph/0508412 Abstract: Investigating the spectral and temporal characteristics of the X-rays coming from Sagittarius A* (Sgr A*) is essential to our development of a more complete understanding of the emission mechanisms in this supermassive black hole located at the center of our Galaxy. Several X-ray flares with varying durations and spectral features have already been observed from this object. Here we present the results of two long XMM observations of the Galactic nucleus carried out in 2004, for a total exposure time of nearly 500 ks. During these observations we detected two flares from Sgr A* with peak 2-10 keV luminosities about 40 times (L_X 9 * 10^34 erg/s) above the quiescent luminosity: one on 2004 March 31 and another on 2004 August 31. The first flare lasted about 2.5 ks and the second about 5 ks. The combined fit on the Epic spectra yield photon indeces of about 1.5 and 1.9 for the first and second flare respectively. This hard photon index strongly suggests the presence of an important population of non-thermal electrons during the event and supports the view that the majority of flaring events tend to be hard and not very luminous. ------------------------------------------------------------------------ Email : belanger@cea.fr Title : A Persistent High-energy Flux from the Heart of the Milky Way: Integral's view of the Galactic Center Author(s): G. Belanger(1,2), A. Goldwurm(1,2), M. Renaud(1,2), R. Terrier(1,2), F. Melia(3), N. Lund(4), J. Paul(1,2), G. Skinner(5), F. Yusef-Zadeh(6) Institute: (1) Service d'Astrophysique, DAPNIA/DSM/CEA, 91191 Gif-sur-Yvette, France (2) Unite mixte de recherche Astroparticule et Cosmologie, 11 place Berthelot, 75005 Paris, France (3) Physics Dept. and Stewart Observatory, Univerity of Arizona, Tucson, AZ 85721, USA (4) Danish National Space Center, Juliane Maries vej 30, Copenhagen, Denmark (5) CESR, Toulouse Cedex 4, France (6) Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208 Paper : ApJ accepted EPrint : astro-ph/0508128 Abstract: Highly sensitive imaging observations of the Galactic center (GC) at high energies with an angular resolution of order 10 arcminutes, is a very recent development in the field of high-energy astrophysics. The Ibis/Isgri imager on the Integral observatory detected for the first time a hard X-ray source, IGR, located within 1 arcminute of Sagittarius A^* (Sgr A*) over the energy range 20-100 keV. Here we present the results of a detailed analysis of approximately 7 * 10^6 s of observations of the GC obtained since the launch of Integral in October 2002. Two years and an effective exposure of 4.7 * 10^6 s have allowed us to obtain more stringent positional constraints on this high-energy source and to construct its spectrum in the range 20-400 keV. Furthermore, by combining the Isgri spectrum with the total X-ray spectrum corresponding to the same physical region around Sgr A* from XMM data, and collected during part of the gamma-ray observations, we constructed and present the first accurate wide band high-energy spectrum for the central arcminutes of the Galaxy. Our complete and updated analysis of the emission properties of the Integral source shows that it is faint but persistent with no variability above 3 sigma , contrary to what was alluded to in our first paper. This result, in conjunction with the spectral characteristics of the soft and hard X-ray emission from this region, suggests that the source is most likely not point-like but, rather, that it is a compact, yet diffuse, non-thermal emission region. The centroid of IGR is estimated to be R.A. = 17^h45^m42^s.5, decl. = -28^o59'28'' (J2000), offset by 1' from the radio position of Sgr A* and with a positional uncertainty of 1'. Its 20-400 keV luminosity at 8 kpc is L = (5.37 +/- 0.21) * 10^35 erg/s. A 3 sigma upper limit on the flux at the electron-positron annihilation energy of 511 keV from the direction of Sgr A* is set at 1.9 * 10^-4 ph cm^-2 s^-1. Very recently, the Hess collaboration presented the detection of a source of TeV gamma-rays also located within an arcminute of Sgr A*. We present arguments in favor of an interpretation according to which the photons detected by Integral and Hess arise from the same compact region of diffuse emission near the central black hole and that the supernova remnant Sgra East could play an important role as a contributor of very high-energy gamma-rays to the overall spectrum from this region. There is also evidence for hard emission from a region located between the central black hole and the radio Arc near l 0.1^o along the Galactic plane and known to contain giant molecular clouds. ------------------------------------------------------------------------ Email : loris@hal.physast.uga.edu Title : CH 3 GHz Observations of the Galactic Center Author(s): Loris Magnani^1, Susan Zelenik^1, T. M. Dame^2, Ben Engebreth^3 Institute: (1) Department of Physics and Astronomy, The University of Georgia, Athens, GA 30602 (2) Harvard-Smithsonian Center for Astrophysics, 60 Garden St., MS 72, Cambridge, MA 02138 (3) Colorado Center for Astrodynamics Research, University of Colorado at Boulder, Boulder, CO 80309 Paper : ApJ, submitted EPrint : astro-ph/0508523 Abstract: A 3 * 3 map of the Galactic Center was made at 9' resolution and 10' spacing in the CH ^2\Pi_1/2, J=1/2, F=1-1 transition at 3335 MHz. The CH emission shows a velocity extent that is nearly that of the CO(1-0) line, but the CH line profiles differ markedly from the CO. The 3335 MHz CH transition primarily traces low-density molecular gas and our observations indicate that the mass of this component within 30 pc of the Galactic Center is 9 * 10^6 M_o. The CO-H_2 conversion factor obtained for the low-density gas in the mapped region is greater than that thought to apply to the dense molecular gas at the Galactic Center. In addition to tracing the low-density molecular gas at the Galactic Center, the CH spectra show evidence of emission from molecular clouds along the line of sight both in the foreground and background. The scale height of these clouds ranges from 27 - 109 pc, consistent with previous work based on observations of molecular clouds in the inner Galaxy. ------------------------------------------------------------------------ Email : shyman@sbc.edu Title : A New Radio Detection of the Bursting Source GCRT J1745-3009 Author(s): Scott D. Hyman T. Joseph W. Lazio Subhashis Roy Paul S. Ray Namir E. Kassim Institute: (1) Department of Physics and Engineering, Sweet Briar College, Sweet Briar, VA 24595 (2) Remote Sensing Division, Naval Research Laboratory, Washington, DC 20375-5351 (3) ASTRON, P.O. Box 2, 7990 AA Dwingeloo, The Netherlands. (4) E. O. Hulburt Center for Space Research, Naval Research Laboratory, Washington, DC 20375-5352 (5) Remote Sensing Division, Naval Research Laboratory, Washington, DC 20375-5351 Paper : ApJ, submitted EPrint : astro-ph/0508264 Abstract: GCRT J1745-3009 is a transient bursting radio source located in the direction of the Galactic center, discovered in 330 MHz VLA observations from 2002 September 30-October 1 by Hyman et al. We have searched for bursting activity from GCRT J1745-3009 in nearly all of the available 330 MHz VLA observations of the Galactic center since 1989 as well as in 2003 GMRT observations. We report a new radio detection of the source in 330 MHz GMRT data taken on 2003 September 28. A single 0.5 Jy burst was detected, approximately 3* weaker than the five bursts detected in 2002. Due to the sparse sampling of the 2003 observation, only the decay portion of a single burst was detected. We present additional evidence indicating that this burst is an isolated one, but we cannot completely rule out additional undetected bursts that may have occured with the same 77 min. periodicity observed in 2002 or with a different periodicity. Assuming the peak emission was detected, the decay time of the burst, 2 min, is consistent with that determined for the 2002 bursts. Based on the total time for which we have observations, we estimate that the source has a duty cycle of roughly 10%. ------------------------------------------------------------------------ (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 ========================================================================