MX0513-40

C. Jones and W. Forman, Center for Astrophysics, communicate: "An x-ray outburst has been observed, localized to a region of approximately 0o.5 by 10o centered on MX0513-40 = NGC 1851. On 1972 Sept. 19 the source was observed by Uhuru for 15s with a peak rate of one-quarter that of the Crab over the energy range 2-6 keV. The source was not detected above 1 percent of the Crab in observations 5m before and after this event. During the 15s observation the intensity of the source was relatively constant, although the spectrum was observed to harden significantly. This event, taken together with that reported by Grindlay and Heise (IAUC 2879) from 3U 1820-30 = NGC 6624, suggests that x-ray bursts may be a common feature associated with globular clusters, although the longer duration of this event indicates that a variety of temporal behavior is possible. Continued monitoring of this, and other globular clusters, is required to understand the origin of these events."