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

Abstract

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 hour eclipsing binary AC211) and six 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 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.

19 pages, 10 Postscript figures, accepted by New Astronomy

References in corpus (1)

• BeppoSAX study of the broad-band properties of luminous globular cluster X-ray sources

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• Unveiling the core of the Globular Cluster M15 in the Ultraviolet
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• The X-ray source population of the globular cluster M15: Chandra high resolution imaging
• The X-Ray Binary X2127+119 in M15: Evidence for a Very-Low-Mass, Stripped-Giant Companion
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• The Luminous Erupting Dwarf Nova CV1 in the Dense Globular Cluster M15
• NICER observations of type-I X-ray bursts from the ultra-compact X-ray binary M15 X-2