Large-scale radio bubbles around the black hole transient V4641 Sgr

¹ Université Paris Cité, Université Paris-Saclay, CEA, CNRS, AIM F-91191 Gif-sur-Yvette, France
² Astrophysics, Department of Physics, University of Oxford Keble Road Oxford OX1 3RH, UK
³ Department of Astronomy, University of Cape Town Private Bag X3 Rondebosch 7701, South Africa
⁴ Department of Physics and Electronics, Rhodes University PO Box 94 Makhanda 6140, South Africa
⁵ South African Radio Astronomy Observatory, 2 Fir Street Black River Park Observatory 7925, South Africa
⁶ INAF-Osservatorio Astronomico di Roma Via Frascati 33 I-00078 Monte Porzio Catone (RM), Italy
⁷ Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Brera via E. Bianchi 46 23807 Merate (LC), Italy

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 5 September 2025
Accepted: 18 December 2025

Abstract

Context. Black holes (BHs) in microquasars can launch powerful relativistic jets that have the capacity to travel up to several parsecs from the compact object and interact with the interstellar medium. Recently, the detection of large-scale very-high-energy (VHE) gamma-ray emission around the black hole transient V4641 Sgr and other BH-jet systems suggested that jets from microquasars may play an important role in the production of galactic cosmic rays.

Aims. V4641 Sgr is known for its superluminal radio jet discovered in 1999, but no radio counterpart of a large-scale jet has been observed. The goal of this work is to search for a radio counterpart of the extended VHE source.

Methods. We observed V4641 Sgr with the MeerKAT radio telescope at the L and UHF bands and produced deep maps of the field using high dynamic range techniques.

Results. We report the discovery of a large-scale (∼35 pc), bow-tie-shaped, diffuse, radio structure around V4641 Sgr, with similar angular size to the extended X-ray emission discovered by XRISM. However, it is not spatially coincident with the extended VHE emission. After discussing the association of the structure with V4641 Sgr, we investigate the nature of the emission mechanism. We suggest that the bow-tie structure arose from the long-term action of large-scale jets or disk winds from V4641 Sgr. If the emission mechanism is of synchrotron origin, the radio/X-ray extended structure implies acceleration of electrons up to more than 100 TeV as far as tens of parsecs from the black hole.