Occurrence rate of stellar Type II radio bursts from a 100 star-year search for coronal mass ejections

¹ ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
² Kapteyn Astronomical Institute, University of Groningen, Kapteynborg 5419, 9747 AD, Groningen, The Netherlands
³ LUX, Observatoire de Paris, Université PSL, CNRS, 5 Place Jules Janssen, 92190 Meudon, France
⁴ ORN, Observatoire de Paris, CNRS, PSL, Université d’Orléans, Nançay, France
⁵ Centre for Radio Astronomy Techniques and Technologies, Department of Physics and Electronics, Rhodes University, Grahamstown, 6140, South Africa
⁶ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁷ Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
⁸ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
⁹ Centre for Astrophysics Research, Department of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
¹⁰ LIRA, Observatoire de Paris, CNRS, PSL, Sorbonne Université, Université Paris Cité, Meudon, France
¹¹ SRON, Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands

^★ Corresponding author: konijn@astron.nl

Received: 28 February 2025
Accepted: 25 September 2025

Abstract

Coronal mass ejections (CMEs) are major drivers of space weather in the Solar System, but their occurrence rate on other stars is unknown. A characteristic (deca-)metric radio burst with a time-frequency drift, known as a Type II radio burst, is a key observational signature of CMEs. We searched a total of 107 years of stellar data using time-frequency spectra that targeted all known stars within 100 parsecs in the LOFAR Two Metre Sky Survey (LoTSS) up to May 2023. This resulted in the largest unbiased search for circularly polarised stellar Type II metric radio bursts to date, with a typical 3σ sensitivity of 2.5 mJy for an integration time of 1 minute. We detected two drifting stellar radio bursts: the published 2-minute burst from the M dwarf StKM 1-1262 and a new 13-minute burst from the M dwarf LP 215-56. The new burst is characterised by a drift rate of −0.060_−0.002^+0.002 MHz s⁻¹, an average Stokes V flux density of −4.5_−1.3^+1.4 mJy, and a temporal duration of 63₋₁₁⁺³¹ seconds. We constrained the occurrence rate of drifting stellar bursts by calculating Poisson upper and lower limits based on the two drifting bursts. We also fitted a cumulative burst luminosity distribution to the data using the burst detections and the non-detections; this yielded a power law index (α) of −0.7_−0.6^+0.9 and a normalisation point (N) of one burst per year with E > 6.8 × 10¹³ erg s⁻¹ Hz⁻¹. We find an agreement between this and the cumulative luminosity distribution of decametric SOHO/LASCO solar Type II data (α = −0.81 ± 0.06 ± 0.02), which suggests that the current scarcity of detected stellar Type II bursts is likely due to limited sensitivity rather than to the intrinsic rarity of these events. Additionally, we identify 19 circularly polarised stellar radio bursts without a time-frequency drift.