Further observations of recurrent X-ray bursts from the globular cluster NGC 6624*

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Abstract
Twenty-two X-ray bursts from the globular cluster NGC 6624 have been observed during the first four days of an eight-day observation. Identification of the burst source with the persistent source 3U 1820 – 30 located at or near the centre of NGC 6624 is confirmed by the observed correlation between the cessation of bursts on the fourth day and the transition of the intensity of 3U 1820 – 30 from its low to its high state. The intervals between bursts declined during the four days from about 0.14 to 0.09 day which shows that the bursts are not controlled by a precisely periodic mechanism but are, instead, produced by some kind of relaxation oscillation. The fraction of X-rays in the tails of the bursts also declined during the four days which may indicate a progressive change in a scattering cloud around the source as the burst activity approached termination.

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