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Faint X-ray sources in the core of the globular cluster M28

Danner, R. and Kulkarni, S. R. and Saito, Y. and Kawai, N. (1997) Faint X-ray sources in the core of the globular cluster M28. Nature, 388 (6644). pp. 751-753. ISSN 0028-0836.

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Globular clusters, the most ancient stellar groups in our galaxy, are known to contain bright X-ray sources, faint X-ray sources and millisecond pulsars. The bright X-ray sources are neutron stars accreting matter from a companion star, and the millisecond pulsars are believed to be descendants of these sources. But the origin of the faint X-ray sources remains unclear. Here we report satellite-based X-ray observations of the globular cluster M28 which reveal two faint X-ray sources; an extended source slightly offset from the centre of the cluster, and a point source. The point source pulsates with the same period as a well-known 3-millisecond pulsar in M28. The nature of the extended source is more puzzling, however, and its spatial and spectral properties permit a range of plausible models. We argue that this source is either a collection of low-luminosity accreting neutron-star binaries or a synchrotron nebula powered by a recent outburst of energy from an unknown source. Sensitive optical and X-ray observations should be able to distinguish between these two possibilities.

Item Type:Article
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URLURL TypeDescription
Kulkarni, S. R.0000-0001-5390-8563
Kawai, N.0000-0001-9656-0261
Additional Information:© 1997 Macmillan Publishers Ltd. Received 4 February 1997; accepted 1 July 1997. We thank J. Grindlay and F. Verbunt for discussions. R.M.D. and S.R.K. thank NASA for support. This work was partially supported by the Scientific Research Fund of the Japanese Ministry of Education, Science, and Culture.
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Ministry of Education, Science, and Culture (Japan)UNSPECIFIED
Issue or Number:6644
Record Number:CaltechAUTHORS:20150609-074651902
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:58097
Deposited By: Tony Diaz
Deposited On:09 Jun 2015 15:09
Last Modified:09 Mar 2020 13:18

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