X-ray sources in globular clusters

The program of X-ray observations of globular clusters being conducted with the Einstein X-ray observatory is described. A survey of some 30 clusters has been completed using the HRI detector and yielded one new source down to luminosities > 1034 d2 erg s-1 (d is distance in 10 kpc units). Preliminary results are reported for a more sensitive survey (luminosity > approximately 1033 d2 erg s-1) now being conducted with the IPC; four possible new sources have been found in the first 32 clusters observed. A related search for diffuse emission from stars in globular clusters is also in progress using much longer IPC exposures. Detailed studies of several luminous, globular cluster sources, including the X-ray burst from Terzan 2, are described. Finally, the major effort to locate precisely (< approximately 2 arcsec) the X-ray sources with respect to the cluster centers is discussed. Sources of systematic error and the required optical studies of globular cluster structure are reviewed. Preliminary results appear to rule out the possibility that the globular cluster sources are massive black holes, although the statistical tests are somewhat model dependent. Implications of the plausible binary systems for cluster core evolution are mentioned. (Auth.)