An Overabundance of Transient X-ray Binaries within 1 pc of the Galactic Center

M. P. Muno(1,2) E. Pfahl(3) F. K. Baganoff(4) W. N. Brandt(5) A. Ghez(1) J. Lu(1) and M. R. Morris(1)

(1) Department of Physics and Astronomy, University of California, Los Angeles, CA 90095;
(2) Hubble Fellow
(3) Chandra Fellow, Department of Astronomy, University of Virginia, Charlottesville, VA 22904
(4) Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139
(5) Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802

Paper: ApJL submitted

EPrint Server: astro-ph/0412492


During five years of Chandra observations, we have identified seven X-ray transients located within 23 pc of \sgrastar. These sources each vary in luminosity by more than a factor of 10, and have peak X-ray luminosities greater than 5 * 1033 \ergs, which strongly suggests that they are accreting black holes or neutron stars. The peak luminosities of the transients are intermediate between those typically considered outburst and quiescence for X-ray binaries. Remarkably four of these transients lie within only 1 pc of \sgrastar. This implies that, compared to the numbers of similar systems located between 1 and 23 pc, transients are over-abundant by a factor of 20 per unit stellar mass within 1 pc of \sgrastar. It is likely that the excess transient X-ray sources are low-mass X-ray binaries that were produced, as in the cores of globular clusters, by three-body interactions between binary star systems and either black holes or neutron stars that have been concentrated in the central parsec through dynamical friction. Alternatively, they could be high-mass X-ray binaries that formed among the young stars that are present in the central parsec.

Preprints available from the authors at mmuno@astro.UCLA.EDU , or the raw TeX (no figures) if you click here.

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