Proceedings of the International Astronomical Union

Populations of High Energy Sources in Galaxies
Contributed Papers

The discovery of X-ray binaries in the Sculptor Dwarf Spheroidal Galaxy

Thomas J. Maccarone a1, Arunav Kundu a2, Stephen E. Zepf a2, Anthony L. Piro a3 and Lars Bildsten a3a4
a1 School of Physics and Astronomy, University of Southampton, Southampton, SO17 1BJ, UK email:
a2 Department of Physiscs and Astronomy, Michigan State University, East Lansing, MI, USA
a3 Department of Physics, University of California at Santa Barbara, Santa Barbara, CA, USA
a4 Kavli Institute for Theoretical Physics, University of California at Santa Barbara, Santa Barbara, CA, USA

Article author query
maccarone tj   [Google Scholar] 
kundu a   [Google Scholar] 
zepf se   [Google Scholar] 
piro al   [Google Scholar] 
bildsten l   [Google Scholar] 
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We report the results of a deep Chandra survey of the Sculptor dwarf spheroidal galaxy. We find five X-ray sources with $L_X$ of at least $6\times10^{33}$ ergs/sec with optical counterparts establishing them as members of Sculptor. These X-ray luminosities indicate that these sources are X-ray binaries, as no other known class of Galactic point sources can reach 0.5-8 keV luminosities this high. Finding these systems proves definitively that such objects can exist in an old stellar population without stellar collisions. Three of these objects have highly evolved optical counterparts (giants or horizontal branch stars), as do three other sources whose X-ray luminosities are in the range which includes both quiescent low mass X-ray binaries and the brightest magnetic cataclysmic variables. We predict that large area surveys of the Milky Way should also turn up large numbers of quiescent X-ray binaries.

(Published Online May 12 2006)

Key Words: X-rays:binaries – X-rays:galaxies – stars:binaries:close – galaxies:individual:Sculptor dwarf spheroidal – stellar dynamics – stars:Population II.