M dwarfs flares timing & energy from TESS & Swift

Additionally, flare energy budgets are not well understood due to a paucity of simultaneous observations. We present new near-UV (NUV) and optical observations of flares from three M dwarfs obtained at 20s cadence with Swift and the Transiting Exoplanet Survey Satellite (TESS), along with a reanalysis of flares from two M dwarfs in order to explore the energy budget and timing of flares at NUV-optical wavelengths.

We find a 9000K blackbody underestimates the NUV flux by >=2x for 54+/-14% of flares and 14.8x for one flare. We report time lags between the bands of 0.5-6.6min and develop a method to predict the qualitative flare shape and time lag to 36%+/-30% accuracy. The scatter present in optical-NUV relations is reduced by a factor of 2.0+/-0.6 when comparing the total NUV energy with the TESS energy during the FWHM duration due to the exclusion of the Teff ~5000K tail.