  M82 hosts two well-known ultraluminous X-ray sources (ULXs). X-1, an
intermediate-mass black hole (IMBH) candidate, and X-2, an ultraluminous X-ray
pulsar (ULXP). Here we present a broadband X-ray spectral analysis of both
sources based on ten observations made simultaneously with Chandra and NuSTAR.
Chandra provides the high spatial resolution to resolve the crowded field in
the 0.5--8 keV band, and NuSTAR provides the sensitive hard X-ray spectral
data, extending the bandpass of our study above 10 keV. The observations, taken
in the period 2015--2016, cover a period of flaring from X-1, allowing us to
study the spectral evolution of this source with luminosity. During four of
these observations, X-2 was found to be at a low flux level, allowing an
unambiguous view of the emission from X-1. We find that the broadband X-ray
emission from X-1 is consistent with that seen in other ULXs observed in detail
with NuSTAR, with a spectrum that includes a broadened disk-like component and
a high-energy tail. We find that the luminosity of the disk scales with inner
disk temperature as L~T^-3/2 contrary to expectations of a standard accretion
disk and previous results. These findings rule out a thermal state for
sub-Eddington accretion and therefore do not support M82 X-1 as an IMBH
candidate. We also find evidence that the neutral column density of the
material in the line of sight increases with L$_X$, perhaps due to an increased
mass outflow with accretion rate. For X-2, we do not find any significant
spectral evolution, but we find the spectral parameters of the phase-averaged
broadband emission are consistent with the pulsed emission at the highest X-ray
luminosities.
