Radio Burst from a Stellar Coronal Mass Ejection

Abstract

Coronal mass ejections (CMEs) are massive expulsions of magnetised plasma from a star, and are the largest contributors to space weather in the Solar System. CMEs are theorized to play a key role in planetary atmospheric erosion, especially for planets that are close to their host star. However, such a conclusion remains controversial as there has not been an unambiguous detection of a CME from a star outside of our Sun. Previous stellar CME studies have only inferred the presence of a CME through the detection of other types of stellar eruptive events. A signature of a fast CME is a Type II radio burst, which is emitted from the shock wave produced as the CME travels through the stellar corona into interplanetary space. Here we report an analogue to a Type II burst from the early M dwarf StKM 1-1262. The burst exhibits identical frequency, time, and polarisation properties to fundamental plasma emission from a solar Type II burst. We demonstrate the rate of such events with similar radio luminosity from M dwarfs are 0.84$^{+1.94}_{-0.69} \times$10$^{-3}$ per day per star. Our detection implies that we are no longer restricted to extrapolating the solar CME kinematics and rates to other stars, allowing us to establish the first observational limits on the impact of CMEs on exoplanets.

Figures (4)

• Figure 1: Dynamic spectra of the burst for different polarisations and durations. The total intensity dynamic spectrum for the entire 8 h observation is shown in the top panel, with the burst bracketed by two red lines. The burst is centered in the bottom panels, with Stokes I, absolute V, Q, and U shown left to right, respectively. The dynamic spectra of Stokes Q and U are smoothed with a Gaussian filter with a kernel of 1 pixel to enhance the visbility of the fainter emission. Note that the colour scale of Stokes I and V are different to that of Stokes Q and U, as demonstrated by distinct colour bars.
• Figure 1: Reconstruction of the burst assuming ECMI from a high-latitude coronal loop. While the overall drift rate is recovered, it is not possible to recover the observed sub-structure in Figure \ref{['fig:dyn_spec_all']}.
• Figure 2: A ridge-crawler fit to the two different emission lanes evident in the circularly polarised burst. The red lines trace the two fits, and the vertical grey lines demarcate the area over which the fit was searched. The two fits intersect at the lowest frequency channel since that channel contains the largest signal-to-noise at the edge of the band. This is likely a product of the limited bandwidth of our observation.
• Figure 3: Circularly polarised dirty map of StKM 1-1262, imaged over the duration of the $\approx$2 minute burst. The red circle identifies the Gaia Data Release 3 2023AA...674A...1G position of StKM 1-1262 at the time of the LOFAR observation and has a radius of 2$"$, corresponding to the astrometric uncertainty of the radio position. The size and shape of the instantaneous synthesised beam is shown in the bottom left corner.