Serendipitous discovery of radio flaring behaviour from a nearby M dwarf with MeerKAT

TL;DR

This paper reports the serendipitous discovery of a nearby M dwarf star exhibiting radio flaring activity, detected by MeerKAT, with multiwavelength observations confirming its magnetic activity and rapid rotation, demonstrating the capabilities of current radio interferometers.

Contribution

First detection of radio flaring from a nearby M dwarf using MeerKAT, with comprehensive multiwavelength follow-up confirming its magnetic activity and rapid rotation.

Findings

Detected radio flaring at 1.3 GHz with flux up to 590 μJy

Identified the star as a high proper motion M dwarf at 12 pc

Confirmed magnetic activity through Hα emission and rapid rotation

Abstract

We report on the detection of MKT J174641.0$-$321404, a new radio transient found in untargeted searches of wide-field MeerKAT radio images centred on the black hole X-ray binary H1743$-$322. MKT J174641.0$-$321404 is highly variable at 1.3 GHz and was detected three times during 11 observations of the field in late 2018, reaching a maximum flux density of 590 $\pm$ 60 $\mu$Jy. We associate this radio transient with a high proper motion, M dwarf star SCR~1746$-$3214 12 pc away from the Sun. Multiwavelength observations of this M dwarf indicate flaring activity across the electromagnetic spectrum, consistent with emission expected from dMe stars, and providing upper limits on quiescent brightness in both the radio and X-ray regimes. \textit{TESS} photometry reveals a rotational period for SCR~1746$-$3214 of $0.2292 \pm 0.0025$ days, which at its estimated radius makes the star a rapid rotator, comparable to other low mass systems. Dedicated spectroscopic follow up confirms the star as a mid-late spectral M dwarf with clear magnetic activity indicated by strong H$\alpha$ emission. This transient's serendipitous discovery by MeerKAT, along with multiwavelength characterisation, make it a prime demonstration of both the capabilities of the current generation of radio interferometers and the value of simultaneous observations by optical facilities such as MeerLICHT. Our results build upon the literature of of M dwarfs' flaring behaviour, particularly relevant to the habitability of their planetary systems.