Multi-wavelength Monitoring of Stellar Flares in the Active Eclipsing Binary CU Cancri

We present simultaneous optical photometry in the U, B, and V bands with the 85-cm telescope at Xinglong Observatory and L-band radio spectroscopy with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) for a stellar flare on the active eclipsing binary CU Cancri. The flare occurred on 2025 January 11 (UT 16:30–19:30) and lasted for about 52 min, with a bolometric flare energy of 2.6 × 1032 erg. The U-band emission reached its peak earlier than the B and V bands, indicative of wavelength-dependent flare heating. The flare blackbody temperature, estimated from the B- to V-band emission ratio during the flare, increased to 13217 K near the peak and then declined rapidly toward the quiescent photospheric value. No significant radio burst was detected in the FAST L-band dynamic spectra during the optical flare. In addition, we analyse the flare activity of CU Cancri using long-term photometric data from Kepler/K2, from which a total of 532 flare events are identified. The results show that the orbital-phase distribution of the flares is consistent with uniformity and does not exhibit statistically significant orbital-phase dependence. Meanwhile, a power-law fit based on the K2 short-cadence data shows that the flare frequency distribution of CU Cancri is overall consistent with that of typical active M dwarfs. These multi-wavelength observations provide complementary constraints on plasma heating, dynamics, and electron acceleration during stellar flares, and offer new insight into how binarity shapes magnetic activity and space-weather environments in active M-dwarf systems.