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

¹ Scuola Universitaria Superiore IUSS Pavia, Palazzo del Broletto, Piazza della Vittoria 15, 27100 Pavia, Italy
e-mail: andrea.tiengo@iusspavia.it
² Istituto Nazionale di Astrofisica, Istituto di Astrofisica Spaziale e Fisica Cosmica di Milano, Via A. Corti 12, 20133 Milano, Italy
³ Istituto Nazionale di Fisica Nucleare, Sezione di Pavia, Via A. Bassi 6, 27100 Pavia, Italy
⁴ Dipartimento di Fisica “Aldo Pontremoli”, Università degli Studi di Milano, Via G. Celoria 16, 20133 Milano, Italy
⁵ Laboratoire des 2 Infinis – Toulouse (L2IT-IN2P3), Université de Toulouse, CNRS, UPS, 31062 Toulouse Cedex 9, France
⁶ Astronomisches Rechen-Institut. Zentrum für Astronomie der Universität Heidelberg, Mönchhofstrasse 12-14, Heidelberg 69120, Germany
⁷ Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate, Italy
⁸ Department of Physics, University of Milano-Bicocca, Piazza della Scienza 3, 20126 Milano, Italy

Received: 15 November 2021
Accepted: 15 February 2022

Abstract

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.