Radio properties of the quasi-periodic eruption source RXJ1301.9+2747 at parsec scales

¹ Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON M5S3H8, Canada
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
³ Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁴ International Centre for Radio Astronomy Research – Curtin University, GPO Box U1987 Perth, WA 6845, Australia
⁵ Department of Astrophysics, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University, P.O. Box 9010 6500 GL Nijmegen, The Netherlands
⁶ Centro de Astrobiología (CAB), CSIC-INTA, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain

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Received: 24 June 2025
Accepted: 28 September 2025

Abstract

Quasi-periodic eruptions (QPEs) are repeating soft X-ray flares associated with galactic nuclei. Several recent works have found evidence that the accretion flow in the galactic nuclei of QPEs is of recent origin, and that it is unlike canonical active galactic nuclei (AGN). A precursor tidal disruption event has been observed in a few cases. In this work we report new radio observations of the QPE host galaxy RXJ 1301.9+2747 taken at 5.0 GHz with the High Sensitivity Array (HSA), to complement archival 1.7 GHz observations reported previously. Our new observations confirm the presence of a highly compact radio source in RXJ 1301.9+2747, which is smaller than 0.9 × 0.4 pc at 5.0 GHz. The nonsimultaneous very long baseline interferometry (VLBI) compact flux of the source is consistent with a negative spectral index, and thus is similar to the larger non-VLBI scale radio spectral index. Contrary to earlier results at 1.7 GHz, we find the 5 GHz emission offset from the optical Gaia position, which may be due to dust extinction in the host galaxy. In addition, there is a significant offset between the 1.7 and 5.0 GHz data, which may result from astrophysical uncertainties in the calibration source. This sheds new light on the elusive properties of the radio-detected QPE sources. Consistent with previous results, our observations disfavor a star formation or jet-core-region origin of the radio emission. We cannot rule out a reconnection-driven scenario for the radio emission, but we favor a remnant jet or outflow scenario. This is overall in agreement with the radio properties of radio-detected QPE sources at lower angular resolution.