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

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 ∼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 ∼90% right-circularly polarized bursts, some of which last for a few minutes and others of which last longer, ≳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 proper, dedicated, simultaneous radio/optical follow-up is needed to monitor the long-term variability and increase the statistics of bursts, in order to test whether the corotating absorbers detected in the optical can drive the observed radio emission, and whether the occurrence of radio bursts correlates with the rotational phase of either star.