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Astron. Astrophys. 355, 145-154 (2000)

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The orbital period of the recurrent X-ray transient in Terzan 6

J.J.M. in 't Zand 1, A. Bazzano 2, M. Cocchi 2, R. Cornelisse 1,3, J. Heise 1, L. Kuiper 1, E. Kuulkers 1,3, C.B. Markwardt 4, J.M. Muller 1,5, L. Natalucci 2, M.J.S. Smith 1,6, T.E. Strohmayer 4, P. Ubertini 2 and F. Verbunt 3

1 Space Research Organization Netherlands, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
2 Istituto di Astrofisica Spaziale (CNR), Area Ricerca Roma Tor Vergata, Via del Fosso del Cavaliere, 00133 Roma, Italy
3 Astronomical Institute, Utrecht University, P.O. Box 80000, 3508 TA Utrecht, The Netherlands
4 NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771, USA
5 BeppoSAX Science Data Center, Nuova Telespazio, Via Corcolle 19, 00131 Roma, Italy
6 BeppoSAX Science Operation Center, Nuova Telespazio, Via Corcolle 19, 00131 Roma, Italy

Received 6 October 1999 / Accepted 21 December 1999


Four or five new outbursts were detected of the bright X-ray transient GRS 1747-312 in the globular cluster Terzan 6 between 1996 and 1999, through monitoring campaigns with the Wide Field Cameras (WFCs) on BeppoSAX and the Proportional Counter Array (PCA) on RossiXTE . This is the first time that the source is seen to exhibit recurrent outbursts after the discovery in September 1990 with ART-P on Granat . Three target-of-opportunity observations in 1998 and 1999, with the narrow-field instruments on BeppoSAX and the PCA, revealed one sharp drop in the flux which we identify as an eclipse of the compact X-ray source by the companion star. A detailed analysis of WFC data identifies further eclipses and we measure the orbital period at 12.360[FORMULA]0.009 hr. This is consistent with an identification as a low-mass X-ray binary, as suggested already by the association with a globular cluster. The eclipse duration is [FORMULA] hr. This implies that the inclination angle is larger than 74o. The 0.1-200 keV unabsorbed peak luminosity is [FORMULA] erg s-1. The nature of the compact object is unclear.

Key words: stars: individual: GRS 1747-312 – stars: neutron – Galaxy: globular clusters: individual: Terzan 6 – X-rays: bursts

Send offprint requests to: J.J.M. in 't Zand, (jeanz@sron.nl)

© European Southern Observatory (ESO) 2000

Online publication: March 17, 2000