  We extend the relativistic time-dependent thin-disc TDE model to describe
nonthermal ($2-10$ keV) X-ray emission produced by the Compton up-scattering of
thermal disc photons by a compact electron corona, developing analytical and
numerical models of the evolving nonthermal X-ray light curves. In the simplest
cases, these X-ray light curves follow power-law profiles in time. We suggest
that TDE discs act in many respects as scaled-up versions of XRB discs, and
that such discs should undergo state transitions into harder accretion states.
XRB state transitions typically occur when the disc luminosity becomes roughly
one percent of its Eddington value. We show that if the same is true for TDE
discs then this, in turn, implies that TDEs with nonthermal X-ray spectra
should come preferentially from large-mass black holes. The characteristic
hard-state transition mass is $M_{\rm HS} \simeq 2\times10^7 M_\odot$. Hence,
subpopulations of thermal and nonthermal X-ray TDEs should come from
systematically different black hole masses. We demonstrate that the known
populations of thermal and nonthermal X-ray TDEs do indeed come from different
distributions of black hole masses. The null-hypothesis of identical black hole
mass distributions is rejected by a two-sample Anderson-Darling test with a
$p$-value $< 0.01$. Finally, we present a model for the X-ray rebrightening of
TDEs at late times as they transition into the hard state. These models of
evolving TDE light curves are the first to join both thermal and nonthermal
X-ray components in a unified scenario.
