  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 9000 K blackbody.
If superflares are hotter, then the UV emission may be 10X higher than
predicted from the optical. However, it is unknown for how long M-dwarf
superflares reach temperatures above 9000 K. Only a handful of M-dwarf
superflares have been recorded with multi-wavelength high-cadence observations.
We double the total number of events in the literature using simultaneous
Evryscope and TESS 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 min 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 14,000 K
depends on energy. We discover 43% of the flares emit above 14,000 K, 23% emit
above 20,000 K and 5% emit above 30,000 K. The largest and hottest flare
briefly reached 42,000 K. Some do not reach 14,000 K. During superflares, we
estimate M-Earths orbiting <200 Myr stars typically receive a top-of-atmosphere
UV-C flux of ~120 W m^-2 and up to 10^3 W m^-2, 100-1000X the time-averaged XUV
flux from Proxima Cen.
