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 | \dot { P } / P| = 3 \times 10 ^ { -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 \pm 0.2 core radii from the cluster center .