Simultaneous Optical and Radio Observations of a Large Stellar Flare on EV Lac
Hongpeng Lu, Jiale Zhang, Hui Tian, Liyun Zhang, Hechao Chen, Jie Zheng, Junbo Zhang, Jian-Guo Wang, Shun Inoue, Hiroyuki Maehara, Kosuke Namekata
Abstract
Abstract We present simultaneous optical and radio observations of a large stellar flare on the M dwarf EV Lac, captured between 12:00 and 15:00 UT on 2022 October 25. This event was jointly monitored with the 85 cm and 2.16 m optical telescopes at the Xinglong Observatory, the Five-hundred-meter Aperture Spherical Radio Telescope (FAST), and the Transiting Exoplanet Survey Satellite, enabling a comprehensive view of flare energy release and dynamic evolution. The flare persisted for 138 minutes with a bolometric energy exceeding 1.7 × 10 33 erg and exhibited a double-peaked light curve. Temporal H α line profiles show Stark broadening and red asymmetry with a redshift of ∼50 km s −1 near the first flare peak, suggesting downward plasma motion possibly due to chromospheric condensation. Enhanced blue wing emission near the second peak reaches a maximum blueshift of −240 km s −1 , indicating a stellar prominence eruption with an estimated mass of 7.3 × 10 18 –3.3 × 10 19 g. Flare blackbody temperature estimates indicate a peak of 12,500 K during the first peak, oscillating between 5500 K and 8100 K near the second peak, and cooling to 3700 K afterward. FAST radio observations reveal positive frequency-drifting, highly polarized bursts consistent with electron cyclotron maser emission modulated by stellar rotation, indicating magnetically trapped energetic electrons during the flare. This unique observation campaign provides a comprehensive view of plasma heating, plasma motions, and electron acceleration during a large stellar flare, offering new insights into the multiwavelength evolution of flare-related plasma processes in stellar atmospheres.