Polarized, variable radio emission from the scallop-shell binary system DG CVn

TL;DR

This study presents detailed radio observations of the binary star DG CVn, revealing polarized bursts likely caused by electron cyclotron maser emission, and discusses their properties and potential modulation by stellar rotation.

Contribution

It provides the first detailed analysis of radio burst polarization and dynamics in DG CVn, suggesting electron cyclotron maser as the emission mechanism and highlighting the need for further multi-wavelength monitoring.

Findings

Detected highly polarized radio bursts with drift in frequency and time.

Identified a quiescent, weakly polarized gyro-synchrotron component.

Suggested electron cyclotron maser as the likely emission mechanism.

Abstract

DG CVn is an eruptive variable star and represents the closest member of the known sample of complex periodic variables, or scallop-shell stars. Over the years, this M dwarf binary system has shown significant flaring activity at a wide range of frequencies. Here, we present a detailed analysis of $\sim 14$ hours of radio observations of this stellar system, taken with the Karl G.Jansky Very Large Array at band L, centered at 1.5 GHz. In both $7$-hour long observations, we have found a quiescent, weakly polarized component, that could be ascribable to the incoherent, gyro-synchrotron emission coming from the magnetosphere surrounding one or both stars, along with multiple $\sim90\%$ right-circularly polarized bursts, some of which last for a few minutes, while others being longer, $\gtrsim$ 30 minutes. Some of these bursts show a drift in frequency and time, possibly caused due to beaming effects or the motion of the plasma responsible for the emission. We assess the possible modulation of burst frequency with the primary and secondary periods, and discuss the properties of these bursts, favoring electron cyclotron maser over plasma emission as the likely underlying mechanism. We compare DG CVn's dynamic spectrum to other young M dwarfs and find many similarities. A dedicated proper radio/optical simultaneous follow-up is needed to monitor the long-term variability, increase the statistics of bursts, in order to test whether the co-rotating absorbers detected in optical can drive the observed radio emission, and whether the occurrence of radio bursts correlates with the rotational phase of either stars.