Superflares may provide the dominant source of biologically relevant UV radiation to rocky habitable-zone M-dwarf planets (M-Earths), altering planetary atmospheres and conditions for surface life. The combined line and continuum flare emission has usually been approximated by a 9000K blackbody. If superflares are hotter, then the UV emission may be 10 times higher than predicted from the optical. However, it is unknown for how long M-dwarf superflares reach temperatures above 9000K. Only a handful of M-dwarf superflares have been recorded with multiwavelength high-cadence observations. We double the total number of events in the literature using simultaneous Evryscope and Transiting Exoplanet Survey Satellite observations to provide the first systematic exploration of the temperature evolution of M-dwarf superflares. We also increase the number of superflaring M-dwarfs with published time-resolved blackbody evolution by ~10x. We measure temperatures at 2 minutes cadence for 42 superflares from 27 K5-M5 dwarfs. We find superflare peak temperatures (defined as the mean of temperatures corresponding to flare FWHM) increase with flare energy and impulse. We find the amount of time flares emit at temperatures above 14000K depends on energy. We discover that 43% of the flares emit above 14000K, 23% emit above 20000K and 5% emit above 30000K. The largest and hottest flare briefly reached 42000K. Some do not reach 14000 K. During superflares, we estimate M-Earths orbiting <200 Myr stars typically receive a top-of-atmosphere UV-C flux of ~120W/m^2^ and up to 10^3^W/m^2^, 100-1000 times the time-averaged X-ray and UV flux from Proxima Cen.

Cone search capability for table J/ApJ/902/115/table1 (Temperatures of simultaneous flares observed during TESS Cycle 1)