  Based on one-month long MMT time-series observations of the open cluster M37,
we monitored light variations of nearly 2500 red dwarfs and successfully
identified 420 flare events from 312 cluster M dwarf stars. For each flare
light curve, we derived observational and physical parameters, such as flare
shape, peak amplitude, duration, energy, and peak luminosity. We show that cool
stars produce serendipitous flares energetic enough to be observed in the
$r$-band, and their temporal and peak characteristics are almost the same as
those in traditional $U$-band observations. We also found many large-amplitude
flares with inferred $\Delta u > 6$ mag in the cluster sample which had been
rarely reported in previous ground-based observations. Following the ergodic
hypothesis, we investigate in detail statistical properties of flare parameters
over a range of energy ($E_{r}$ $\simeq$ $10^{31}-10^{34}$ erg). As expected,
there are no statistical differences in the distributions of flare timescales,
energies, and frequencies among stars of the same age and mass group. We note
that our sample tend to have longer rise and decay timescales compared to those
seen in field flare stars of the same spectral type and be more energetic.
Flare frequency distributions follow power-law distributions with slopes $\beta
\sim0.62-1.21$ for all flare stars and $\beta \sim0.52-0.97$ for stars with
membership information ($P_{mem} \geq 0.2$). These are in general agreement
with previous works on flare statistics of young open clusters and nearby field
stars. Our results give further support to the classical age-activity
relations.
