Fragments of harmony amid apparent chaos: A closer look at the X-ray quasi-periodic eruptions of the galaxy RX J1301.9+2747

¹ Centro de Astrobiologia (CAB), CSIC-INTA, Camino Bajo del Castillo s/n, Campus ESAC, 28692 Villanueva de la Cañada, Madrid, Spain
² Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA
³ International Centre for Radio Astronomy Research (ICRA), Curtin University, GPO Box U1987 Perth, WA 6845, Australia
⁴ Department of Astronomy/Steward Observatory, University of Arizona, 933 N Cherry Avenue, Tucson, AZ 85721-0065, USA
⁵ Max-Planck-Institut für extraterrestrische Physik (MPE), Giessnbachstrasse 1, 85748 Garching bei München, Germany
⁶ Center for Astrophysics | Harvard & Smithsonian, Cambridge, MA, USA
⁷ Telespazio UK for the European Space Agency (ESA), European Space Astronomy Centre (ESAC), Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
⁸ Dipartimento di Fisica “G. Occhialini”, Università degli Studi di Milano-Bicocca, Piazza della Scienza 3, I-20126 Milano, Italy
⁹ INFN, Sezione di Milano-Bicocca, Piazza della Scienza 3, I-20126 Milano, Italy
¹⁰ INAF – Osservatorio Astronomico di Brera, Via Brera 20, I-20121 Milano, Italy
¹¹ Center for Theoretical Astrophysics and Cosmology, Institute for Computational Science, University of Zurich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
¹² Institut für Astrophysik, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
¹³ Max Planck Institute for Astrophysics (MPA), Karl-Schwarzschild-Strasse 1, D-85748 Garching, Germany
¹⁴ Department of Physics, Anhui Normal University, Wuhu, Anhui 241002, People’s Republic of China
¹⁵ INAF, Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate, (LC), Italy
¹⁶ IRAP, Université de Toulouse, CNRS, UPS, CNES, 9 Avenue du Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
¹⁷ Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spain
¹⁸ Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
¹⁹ Serco for the European Space Agency (ESA), European Space Astronomy Centre (ESAC), Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
²⁰ Max Planck Institute for Radio Astronomy, Auf dem Hügel 69, Bonn 53121, Germany

^⋆ Corresponding author; mgiustini@cab.inta-csic.es

Received: 24 May 2024
Accepted: 2 September 2024

Abstract

Quasi-periodic eruptions (QPEs) are an extreme X-ray variability phenomenon associated with low-mass (M_BH < 10⁷ M_⊙) supermassive black holes (SMBHs). First discovered in the nucleus of the galaxy GSN 069, they have been so far securely detected in five other galaxies, including RX J1301.9+2747. When detected, the out-of-QPE emission (quiescence) is consistent with the high-energy tail of thermal emission from an accretion disk. In this article we present the X-ray properties of RX J1301.9+2747, both in quiescence and during QPEs, and complement this information with radio observations. We analyze X-ray data taken during five XMM-Newton observations between 2000 and 2022. The last three observations were taken in coordination with radio observations with the Karl G. Jansky Very Large Array. We also made use of EXOSAT, ROSAT, and Chandra archival observations taken between 1983 and 2009. XMM-Newton detected 34 QPEs of which eight have significantly lower amplitudes than the others. No correlated radio/X-ray variability was observed during QPEs. In terms of timing properties, the QPEs in RX J1301.9+2747 do not exhibit the striking regularity observed in the discovery source GSN 069. In fact there is no clear repetition pattern between QPEs: the average time separation between their peaks is about four hours, but it can be as short as one, and as long as six hours. The QPE spectral properties of RX J1301.9+2747 as a function of energy are, however, very similar to those of GSN 069 and of other QPE sources. During their evolution, X-ray QPEs follow a hysteresis pattern in the temperature-luminosity plane, with a hotter rise than decay. The quiescent emission of RX J1301.9+2747 is more complex than that of GSN 069, as it requires a soft X-ray excess-like component in addition to the thermal emission from the accretion disk. Its long-term X-ray quiescent flux variations are of a low amplitude and not strictly monotonic, with a general decay over the course of ∼22 years. We discuss our observational results in terms of some of the ideas and models that have been proposed so far for the physical origin of QPEs.