X-ray and UV variability in the core of M15: the nature of X2127+119/AC211

The prototypical post-core-collapse globular cluster M15 provides an ideal environment for the formation of exotic binaries, it being already known to contain a luminous LMXB (X2127+119, optically identified with the 17.1-h eclipsing binary AC211) and 6 millisecond-pulsars in the core. However, the X-ray properties of X2127+119 are strange in that it appears to be a high inclination accretion disc corona source (ADC) from which we only see scattered X-radiation, and yet it has produced extremely luminous type I X-ray bursts, which may or may not have come from AC211. We have therefore examined the similar to 5-year RXTE/ASM light curve of this object in order to search for long-term modulations which might shed light on this unusual behaviour, and which led to our discovery of further X-ray bursts. Furthermore, we have used archival HST UV images of the M15 core to search for other variable objects which might indicate the presence of a second LMXB. From these we have found one highly variable (>5 mag) object which we interpret as a dwarf nova. (C) 2002 Published by Elsevier Science B.V.