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Title: A DEEP CHANDRA X-RAY LIMIT ON THE PUTATIVE IMBH IN OMEGA CENTAURI

We report a sensitive X-ray search for the proposed intermediate-mass black hole (IMBH) in the massive Galactic cluster, {omega} Centauri (NGC 5139). Combining Chandra X-ray Observatory data from Cycles 1 and 13, we obtain a deep ({approx}291 ks) exposure of the central regions of the cluster. We find no evidence for an X-ray point source near any of the cluster's proposed dynamical centers, and place an upper limit on the X-ray flux from a central source of f{sub X}(0.5-7.0 keV) {<=}5.0 Multiplication-Sign 10{sup -16} erg cm{sup -2} s{sup -1}, after correcting for absorption. This corresponds to an unabsorbed X-ray luminosity of L{sub X}(0.5-7.0 keV) {<=}1.6 Multiplication-Sign 10{sup 30} erg s{sup -1}, for a cluster distance of 5.2 kpc, Galactic column density N{sub H} = 1.2 Multiplication-Sign 10{sup 21} cm{sup -2}, and power-law spectrum with {Gamma} = 2.3. If a {approx}10{sup 4} M{sub sun} IMBH resides in the cluster's core, as suggested by some stellar dynamical studies, its Eddington luminosity would be L{sub Edd} {approx}10{sup 42} erg s{sup -1}. The new X-ray limit would then establish an Eddington ratio of L{sub X}/L{sub Edd} {approx}< 10{sup -12}, a factor of {approx}10 lower than even the quiescent state of our Galaxy's notoriously inefficientmore » supermassive black hole Sgr A*, and imply accretion efficiencies as low as {eta} {approx}< 10{sup -6}-10{sup -8}. This study leaves open three possibilities: either {omega} Cen does not harbor an IMBH or, if an IMBH does exist, it must experience very little or very inefficient accretion.« less
Authors:
 [1] ;  [2] ;  [3] ; ;  [4] ; ;  [5]
  1. Center for Interdisciplinary Exploration and Research in Astrophysics, Physics and Astronomy Department, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (United States)
  2. Department of Physics and Astronomy, San Francisco State University, 1600 Holloway Ave., San Francisco, CA 94132 (United States)
  3. Department of Physics, University of Alberta, Room 238 CEB, Edmonton, AB T6G 2G7 (Canada)
  4. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
  5. Department of Astronomy, Indiana University, 727 E. Third St., Bloomington, IN 47405 (United States)
Publication Date:
OSTI Identifier:
22136571
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 773; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; ACCRETION DISKS; BLACK HOLES; DISTANCE; GALAXIES; KEV RANGE; LUMINOSITY; POINT SOURCES; SPECTRA; STAR CLUSTERS; TELESCOPES; X RADIATION