An X-ray survey of globular clusters and their X-ray luminosity function
Abstract
An X-ray survey of 71 globular clusters has been conducted with the Einstein Observatory. Fourteen new X-ray sources have been discovered in seven globular clusters; this brings to 18 the total number of known X-ray emitting globular clusters in the Galaxy. Multiple sources have been detected in NGC 5139 (ω Cen) and NGC 6656 (M22). Quiescent emission has been detected from the transient MX 1746-20 located in the cluster NGC 6440. The maximum likelihood luminosity function has been derived for globular cluster X-ray sources. It is bimodal, showing two distinct classes of globular cluster X-ray sources. Sources with Lx ⪆ 1036ergs s-1 are probably accreting neutron star systems; all of the known globular cluster bursters fall into this category. It is suggested that the dim sources, with Lx ⪉ 10-34.5 ergs s-1, be identified as binary systems with white dwarfs as the compact members.
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