Kavli Affiliate: Jing Wang
| First 5 Authors: Hua-Li Li, Jing Wang, Li-Ping Xin, Jian-Ying Bai, Xu-Hui Han
| Summary:
Stellar white-light flares are believed to play an essential role on the
physical and chemical properties of the atmosphere of the surrounding
exoplanets. Here we report an optical monitoring campaign on the nearby flaring
system EI~Cnc carried out by the Ground-based Wide Angle Cameras (GWAC) and its
dedicated follow-up telescope. A superflare, coming from the brighter component
EI~CncA, was detected and observed, in which four components are required to
properly model the complex decay light curve. The lower limit of flare energy
in the $R-$band is estimated to be $3.3times10^{32}$ ergs. 27 flares are
additionally detected from the GWAC archive data with a total duration of 290
hours. The inferred cumulative flare frequency distribution follows a quite
shallow power-law function with a slope of $beta=-0.50pm 0.03$ over the
energy range between $10^{30}$ and $10^{33}$ erg, which reinforces the trend
that stars cooler than M4 show enhanced superflare activity. The flares
identified in EI~Cnc enable us to extend the $tau-E$ relationship previously
established in the white-light superflares of solar-type stars down to an
energy as low as $sim10^{30}$erg (i.e., by three orders): $taupropto
E^{0.42pm0.02}$, which suggests a common flare mechanism for stars with a type
from M to solar-like, and implies an invariant of $B^{1/3}upsilon_{rm A}$ in
the white-light flares.
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