The hard quiescent spectrum of the neutron-star X-ray transient EXO 1745-248 in the globular cluster Terzan 5

Rudy Wijnands; Craig O. Heinke; David Pooley; Peter D. Edmonds; Walter H. G. Lewin; Jonathan E. Grindlay; Peter G. Jonker; Jon M. Miller

doi:10.1086/426127

arXiv · astro-ph/0310144

The hard quiescent spectrum of the neutron-star X-ray transient EXO 1745-248 in the globular cluster Terzan 5

Rudy Wijnands·Craig O. Heinke·David Pooley·Peter D. Edmonds·Walter H. G. Lewin·Jonathan E. Grindlay·Peter G. Jonker·Jon M. Miller

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Abstract

We present a Chandra observation of the globular cluster Terzan 5 during times when the neutron-star X-ray transient EXO 1745-248 located in this cluster was in its quiescent state. We detected the quiescent system with a (0.5-10 keV) luminosity of ~2 x 10^{33} ergs/s. This is similar to several other neutron-star transients observed in their quiescent states. However, the quiescent X-ray spectrum of EXO 1745--48 was dominated by a hard power-law component instead of the soft component that usually dominates the quiescent emission of other neutron-star X-ray transients. This soft component could not conclusively be detected in EXO 1745-248 and we conclude that it contributed at most 10% of the quiescent flux in the energy range 0.5-10 keV. EXO 1745-248 is only the second neutron-star transient whose quiescent spectrum is dominated by the hard component (SAX J1808.4-3658 is the other one). We discuss possible explanations for this unusual behavior of EXO 1745-248, its relationship to other quiescent neutron-star systems, and the impact of our results on understanding quiescent X-ray binaries. We also discuss the implications of our results on the way the low-luminosity X-ray sources in globular clusters are classified.

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Rudy Wijnands, Craig O. Heinke, David Pooley, Peter D. Edmonds, Walter H. G. Lewin, Jonathan E. Grindlay, Peter G. Jonker, Jon M. Miller. 2004-09-22. The hard quiescent spectrum of the neutron-star X-ray transient EXO 1745-248 in the globular cluster Terzan 5. https://doi.org/10.1086/426127

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