Simultaneous Detection of Optical Flares of the Magnetically Active M Dwarf Wolf 359

TL;DR

This study reports the detection and analysis of 13 optical flares from the magnetically active M dwarf Wolf 359 over a week, providing insights into flare energies, rates, and profiles through simultaneous multi-telescope observations.

Contribution

First simultaneous multi-telescope optical monitoring of Wolf 359's flares, improving flare profile estimates and informing future observational strategies.

Findings

Detected 13 flares with energies ≥5×10^29 erg.

Observed a major flare with nearly 10^33 erg energy.

Provided improved flare profile measurements through dual-telescope data.

Abstract

We present detections of stellar flares of Wolf\,359, an M6.5 dwarf in the solar neighborhood (2.41~pc) known to be prone to flares due to surface magnetic activity. The observations were carried out from 2020 April 23 to 29 with a 1-m and a 0.5-m telescope separated by nearly 300~km in Xinjiang, China. In 27~hr of photometric monitoring, a total of 13 optical flares were detected, each with a total energy of $\gtrsim 5 \times 10^{29}$~erg. The measured event rate of about once every two hours is consistent with those reported previously in radio, X-ray and optical wavelengths for this star. One such flare, detected by both telescopes on 26 April, was an energetic event with a released energy of nearly $10^{33}$~erg. The two-telescope lightcurves of this major event sampled at different cadences and exposure timings enabled us to better estimate the intrinsic flare profile, which reached a peak of up to 1.6 times the stellar quiescent brightness, that otherwise would have been underestimated in the observed flare amplitudes of about $0.4$ and $0.8$, respectively, with single telescopes alone. The compromise between fast sampling so as to resolve a flare profile versus a longer integration time for higher photometric signal-to-noise provides a useful guidance in the experimental design of future flare observations.