The X-ray source population of the globular cluster M15: Chandra high-resolution imaging
Charles, P. A.; Davies, M. B.; Naylor, T.; Kong, A. K. H.; Hakala, P.; van Zyl, L.; Hannikainen, D. C.; Homer, L.
United Kingdom, Finland, United States, Sweden
Abstract
The globular cluster M15 was observed on three occasions with the High Resolution Camera on-board Chandra in 2001 in order to investigate the X-ray source population in the cluster centre. After subtraction of the two bright central sources, four faint sources were identified within 50 arcsec of the core. One of these sources is probably the planetary nebula K648, making this the first positive detection of X-rays from a planetary nebula inside a globular cluster. Another two are identified with UV variables (one previously known), which we suggest are cataclysmic variables (CVs). The nature of the fourth source is more difficult to ascertain, and we discuss whether it is possibly a quiescent soft X-ray transient or also a CV.