======================================================================== G C N E W S * Newsflash * - The Newsletter for Galactic Center Research - gcnews@mpifr-bonn.mpg.de http://www.mpifr-bonn.mpg.de/gcnews ======================================================================== Vol. 13, No. 15 Jul 10, 2001 Recently submitted papers: -------------------------- 1) X-ray Bursts from the Source A1742-294 in the Galactic-Center Region (A.A. Lutovinov et al., Astronomy L.) 2) Large scale ionization of the Radio Arc region by the Quintuplet and the Arches clusters (Rodriguez-Fernandez et al., A&A) ------------------------------------------------------------------------ Email : aal@hea.iki.rssi.ru Title : X-ray Bursts from the Source A1742-294 in the Galactic-Center Region Author(s): A.A.Lutovinov(1), S.A.Grebenev(1), M.N.Pavlinsky(1), R.A.Sunyaev(1,2) Institute: (1)Space Research Institute, Russian Academy of Sciences, Profsoyuznaya str., 84/32, Moscow, 117810 Russia (2)Max-Planck Institut fuer Astrophysik, Karl-Schwarzschild-Str. 1, 85740, Garching, Germany Paper : Astronomy Letters, 2001, v.27, N8 EPrint : astro-ph/0107014 Abstract: We present results of observations of the X-ray burster A1742-294 near the Galactic center with the ART-P telescope onboard the Granat observatory. The shape of its persistent spectra was well described by the model of bremsstrahlung from optically thin plasma, and it had remained essentially unchanged over 2.5 years of observations. We show that the mean interval between X-ray bursts from the source is several times shorter than assumed previously, and that the burst profile itself depends on the flux during the burst. We analyze in detail the strong X-ray burst detected from this source on October 18, 1990, and trace the evolution of its luminosity and radiation temperature. ------------------------------------------------------------------------ Email : nemesio@oan.es Title : Large scale ionization of the Radio Arc region by the Quintuplet and the Arches clusters Author(s): Nemesio J. Rodriguez-Fernandez, Jesus Martin-Pintado, and Pablo de Vicente Institute: Observatorio Astronomico Nacional, Instituto Geografico Nacional, Apdo. 1143, E28800 Alcala de Henares, Madrid, Spain Paper : A&A, in press EPrint : astro-ph/0107156 Abstract: We present an analysis of selected fine structure lines (NeII 12.8 micron, NeIII 15.6 micron, SIII 18.7 and 33.5 micron, OIII 52 and 88 micron, NII 122 micron and NIII 57 micron ) observed with the Infrared Space Observatory (ISO) toward the Radio Arc in the Galactic center region (GCR). Most of the data were retrieved from the ISO Data Archive. We study the density of the ionized gas and the large scale ionization structure in a region of 30*30 pc^2 by means of the OIII 52 micron /88 micron, SIII 18.7 micron /33.5 micron, NeIII 15.6 micron /NeII 12.8 micron and NIII 57 micron /NII 122 micron line ratios. The electron densities (n_e) derived from the OIII lines ratio indicate the presence of diffuse ionized material with n_e of 10^1.8-2.6 cm^-3. The NeIII 15.6 micron /NeII 12.8 micron and NIII 57 micron /NII 122 micron line ratios vary from source to source from 0.05 to 0.30 and from 0.3 to 2.5, respectively. The NIII 57/NII 122 micron ratio show two clear gradients, one pointing toward the Quintuplet cluster and the other pointing toward the Arches cluster. We have used a simple model to explain the ionization structure observed in the NIII/NII and NeIII/NeII lines ratios. The model shows that the large scale ionization of the whole region can be accounted for by the UV radiation produced by the Quintuplet and the Arches cluster. Any other ionization mechanism should play a minor role. We also investigate the influence of the clusters on the bubble of warm dust (hereafter Radio Arc Bubble, RAB) seen in the Midcourse Space Experiment (MSX) infrared images. We find that the warm dust is well correlated with the ionized gas indicating that the dust is also heated by the radiation from both clusters. Furthermore, the elliptical rather than circular symmetry of some structures like the Thermal Filaments can also be explained when one considers the combined effects of both the Arches and the Quintuplet clusters. We have also found that the RAB is filled with continuum emission of hard X rays and with emission from the 6.4 keV line of neutral or low ionized Fe. We briefly discuss the implications of these findings on the structure and morphology of the GCR interstellar medium and the possible origin of the RAB. ------------------------------------------------------------------------ (Older versions of the Newsflash can be found at the gcnews web-page) ======================================================================== Edited by Angela Cotera Heino Falcke & Sera Markoff (cotera@as.arizona.edu) (hfalcke,smarkoff@mpifr-bonn.mpg.de) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - For Abstract submission please send the (La)Tex file of your paper to gcnews@mpifr-bonn.mpg.de ========================================================================