Bright radio emission from an ultraluminous stellar-mass microquasar in M31

TL;DR

This paper reports the discovery of a bright, variable radio and X-ray source in M31, likely powered by near-Eddington accretion onto a stellar-mass black hole, providing insights into jet formation in ultraluminous X-ray sources.

Contribution

It presents the first detailed radio and X-ray observations of a microquasar in M31, linking accretion near the Eddington limit to jet ejection in an extragalactic context.

Findings

High radio luminosity with rapid variability indicates a compact, accreting black hole.

The source exceeds 10^39 erg/s in luminosity, classifying it as ultraluminous.

Observations suggest a causal connection between accretion and jet emission.

Abstract

A subset of ultraluminous X-ray sources (those with luminosities < 10^40 erg/s) are thought to be powered by the accretion of gas onto black holes with masses of ~5-20 M_solar, probably via an accretion disc. The X-ray and radio emission are coupled in such Galactic sources, with the radio emission originating in a relativistic jet thought to be launched from the innermost regions near the black hole, with the most powerful emission occurring when the rate of infalling matter approaches a theoretical maximum (the Eddington limit). Only four such maximal sources are known in the Milky Way, and the absorption of soft X-rays in the interstellar medium precludes determining the causal sequence of events that leads to the ejection of the jet. Here we report radio and X-ray observations of a bright new X-ray source whose peak luminosity can exceed 10^39 erg/s in the nearby galaxy, M31. The radio luminosity is extremely high and shows variability on a timescale of tens of minutes, arguing that the source is highly compact and powered by accretion close to the Eddington limit onto a stellar mass black hole. Continued radio and X-ray monitoring of such sources should reveal the causal relationship between the accretion flow and the powerful jet emission.