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Astron. Astrophys. 329, L37-L40 (1998)

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Letter to the Editor

Detection of X-ray bursts in the globular cluster NGC 6652

J.J.M. in 't Zand 1, F. Verbunt 2, J. Heise 1, J.M. Muller 1, 3, A. Bazzano 4, M. Cocchi 4, L. Natalucci 4 and P. Ubertini 4

1 Space Research Organization Netherlands, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
2 Astronomical Institute, P.O.Box 80000, 3508 TA Utrecht, The Netherlands
3 BeppoSAX Science Data Center, Nuova Telespazio, Via Corcolle 19, I-00131 Roma, Italy
4 Istituto di Astrofisica Spaziale (CNR), Via Fosso del Cavaliere, I-00133 Roma, Italy

Received 2 October 1997 / Accepted 24 October 1997

Abstract

Two type I X-ray bursts were detected from a position consistent with the transient X-ray source in NGC 6652 with the Wide Field Camera of the BeppoSAX satellite, strongly suggesting that this transient is a neutron star. Our detection brings to ten the number of X-ray sources in globular clusters in which a type I X-ray burst has been seen, out of twelve known bright sources. The statistical evidence that the fraction of low-mass X-ray binaries which contain a black hole accretor is smaller in globular clusters than in the galactic disk is suggestive, but as yet not compelling.

Key words: X-rays: bursts – globular clusters: NGC 6652

Send offprint requests to: J.J.M. in 't Zand

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© European Southern Observatory (ESO) 1998

Online publication: December 8, 1997
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