Because these systems are so bright in X-rays, the globular cluster population is completely known – we expect no new LMXBs to be discovered in the globular cluster system (unless more multiple sources are resolved from these 13 sources). The 13 sources are in 12 separate clusters. Three have orbital periods greater than a few hours, four ultracompact systems have measured orbital periods less than 1 hour, and six have undetermined orbital periods. The period of X1746-370 in NGC 6441 has recently been measured at using the Rossi X-ray Timing Explorer (RXTE) . A member of the ultracompact group, 4U 1820-30 (X1820-303) in the globular cluster NGC 6624, has an orbital period of 11 minutes . This is the shortest known orbital period of any binary and most certainly indicates a degenerate companion. The orbital period, X-ray luminosity, and host globular clusters for these systems are given in Table 1.
The improved resolution of Chandra allows for the possibility of identifying optical counterparts to LMXBs. If an optical counterpart can be found, a number of additional properties and constraints for these objects can be determined through observations in other wavelengths. In particular, the orbital parameters and the nature of the secondary can be determined. So far, optical counterparts have been found for X0512–401 in NGC 1851 , X1745–203 in NGC 6440 , X1746–370 in NGC 6441 , X1830–303 in NGC 6624 , X1832–330 in NGC 6652 [48, 99], X1850–087 in NGC 6712 [38, 11, 169], X1745-248 in Terzan 5 , and both LMXBs in NGC 7078 [8, 239]. Continued X-ray observations will also further elucidate the nature of these systems .
The 13 bright LMXBs are thought to be active members of a larger population of lower luminosity quiescent low mass X-ray binaries (qLMXBs) . Early searches performed with ROSAT data (which had a detection limit of ) revealed roughly 30 sources in 19 globular clusters . A more recent census of the ROSAT low luminosity X-ray sources, published by Verbunt , lists 26 such sources that are probably related to globular clusters. Recent observations with the improved angular resolution of Chandra have begun to uncover numerous low luminosity X-ray candidates for CVs [88, 89, 99, 110, 100, 101, 54, 55, 75, 182, 183]. For a reasonably complete discussion of recent observations of qLMXBs in globular clusters, see Verbunt and Lewin  or Webb and Barret  and references therein.
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