Recurrent X-ray flares of the black hole candidate in the globular cluster RZ 2109 in NGC 4472

We report the systematic analysis of the X-ray observations of the ultraluminous X-ray source XMMU J122939.7+075333 located in the globular cluster RZ 2109 in the Virgo galaxy NGC 4472 . The inclusion of observations and time intervals ignored in previous works and the careful selection of extraction regions and energy bands have allowed us to identify new flaring episodes, in addition to those that made it one of the best black hole candidates in globular clusters. Although most observations are too short and sparse to recognize a regular pattern, the spacing of the three most recent X-ray flares is compatible with a recurrence time of ∼34 h. If confirmed by future observations, this behavior together with the soft spectrum of the X-ray flares would be strikingly similar to the quasiperiodic eruptions recently discovered in galactic nuclei. Following one of the possible interpretations of these systems and of a peculiar class of extragalactic X-ray transients, we explore the possibility that XMMU J122939.7+075333 might be powered by the partial disruption of a white dwarf by an intermediate-mass ( M ∼ 700 M ⊙ ) black hole.