M dwarf stars are known for their vigorous flaring .
This flaring could impact the climate of orbiting planets , making it important to characterize M dwarf flares at the short wavelengths that drive atmospheric chemistry and escape .
We conducted a far-ultraviolet flare survey of 6 M dwarfs from the recent MUSCLES ( Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems ) observations , as well as 4 highly-active M dwarfs with archival data .
When comparing absolute flare energies , we found the active-M-star flares to be about 10 \times more energetic than inactive-M-star flares .
However , when flare energies were normalized by the star ’ s quiescent flux , the active and inactive samples exhibited identical flare distributions , with a power-law index of - 0.76 ^ { +0.1 } _ { -0.09 } ( cumulative distribution ) .
The rate and distribution of flares are such that they could dominate the FUV energy budget of M dwarfs , assuming the same distribution holds to flares as energetic as those cataloged by Kepler and ground-based surveys .
We used the observed events to create an idealized model flare with realistic spectral and temporal energy budgets to be used in photochemical simulations of exoplanet atmospheres .
Applied to our own simulation of direct photolysis by photons alone ( no particles ) , we find the most energetic observed flares have little effect on an Earth-like atmosphere , photolyzing \sim 0.01 % of the total O _ { 3 } column .
The observations were too limited temporally ( 73 h cumulative exposure ) to catch rare , highly energetic flares .
Those that the power-law fit predicts occur monthly would photolyze \sim 1 % of the O _ { 3 } column and those it predicts occur yearly would photolyze the full O _ { 3 } column .
Whether such energetic flares occur at the rate predicted is an open question .