EDP Sciences
Free access
Volume 406, Number 1, July IV 2003
Page(s) 233 - 243
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20030681

A&A 406, 233-243 (2003)
DOI: 10.1051/0004-6361:20030681

Bursts, eclipses, dips and a refined position for the luminous low-mass X-ray binary in the globular cluster Terzan 6

J. J. M. in 't Zand1, 2, F. Hulleman2, C. B. Markwardt3, 4, M. Méndez1, E. Kuulkers5, R. Cornelisse1, 2, J. Heise1, 2, T. E. Strohmayer3 and F. Verbunt2

1  SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
2  Astronomical Institute, Utrecht University, PO Box 80000, 3508 TA Utrecht, The Netherlands
3  NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771, USA
4  Dept. of Astronomy, University of Maryland, College Park, MD 20742, USA
5  ESA-ESTEC, Science Operations & Data Systems Division, SCI-SDG, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands

(Received 21 February 2003 / Accepted 6 May 2003 )

GRS 1747-312 is a bright transient X-ray source in the globular cluster Terzan 6 with quasi-periodic outbursts approximately every 4.5 months. We carried out 2-60 keV target-of-opportunity observations during eight outbursts with the Proportional Counter Array on the RXTE satellite, for a total exposure time of 301 ks, and detect the first unambiguous thermonuclear X-ray bursts from this source. This identifies the compact accretor in this binary as a neutron star. The neutron star identification implies that twelve out of thirteen luminous (above 10 36 erg s -1) X-ray sources in Galactic globular clusters harbor neutron stars, with AC211's nature (in M15) remaining elusive. We observed 24 transitions of eclipses of the X-ray emitting region by the companion star and are able to improve the accuracy of the orbital period by a factor of 10 4. The period is P=0.514980303(7) d. We do not detect a period derivative with an upper limit of $\vert\dot{P}/P\vert=3\times10^{-8}$ yr -1. Archival Chandra data were analyzed to further refine the X-ray position, and the cluster's center of gravity was re-determined from optical data resulting in a correction amounting to 2 core radii. We find that GRS 1747-312 is $0.2\pm0.2$ core radii from the cluster center.

Key words: accretion, accretion disks -- globular clusters: individual: Terzan 6 -- X-rays: binaries -- X-rays: bursts -- X-rays: individual: GRS 1747-312

Offprint request: J. J. M. in 't Zand, jeanz@sron.nl

© ESO 2003