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

Published online by Cambridge University Press:  12 May 2006

Thomas J. Maccarone ,
Arunav Kundu ,
Stephen E. Zepf ,
Anthony L. Piro  and
Lars Bildsten
Thomas J. Maccarone
Affiliation:
School of Physics and Astronomy, University of Southampton, Southampton, SO17 1BJ, UK email: tjm@phys.soton.ac.uk
Arunav Kundu
Affiliation:
Department of Physiscs and Astronomy, Michigan State University, East Lansing, MI, USA
Stephen E. Zepf
Affiliation:
Department of Physiscs and Astronomy, Michigan State University, East Lansing, MI, USA
Anthony L. Piro
Affiliation:
Department of Physics, University of California at Santa Barbara, Santa Barbara, CA, USA
Lars Bildsten
Affiliation:
Department of Physics, University of California at Santa Barbara, Santa Barbara, CA, USA Kavli Institute for Theoretical Physics, University of California at Santa Barbara, Santa Barbara, CA, USA
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Abstract

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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.

Keywords

X-rays:binaries – X-rays:galaxies – stars:binaries:close – galaxies:individual:Sculptor dwarf spheroidal – stellar dynamics – stars:Population II
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 1 , Symposium S230: Populations of High Energy Sources in Galaxies , August 2005 , pp. 175 - 179
Copyright
2006 International Astronomical Union