  We present a relativistic disk-corona model for a steady state advective
accretion disk to explain the UV to X-ray spectral index $\alpha_{\text{OX}}$
evolution of \textbf{four} tidal disruption event (TDE) sources XMMSL2J1446,
XMMSL1J1404, XMMSL1J0740, \textbf{and AT2018fyk}. The viscous stress in our
model depends on gas ($P_g$) and total ($P_t$) pressures as $\tau_{r\phi}
\propto P_g^{\mu} P_t^{1-\mu}$, where $\mu$ is a constant. We compare various
steady and time-dependent sub-Eddington TDE accretion models along with our
disk-corona model to the observed $\alpha_{\text{OX}}$ of TDE sources and find
that the disk-corona model agrees with the observations better than the other
models. We find that $\mu$ is much smaller than unity for TDE sources
XMMSL2J1446, XMMSL1J1404, and XMMSL1J0740. We also compare the relativistic
model with a non-relativistic disk-corona model. The relativistic accretion
dynamics reduce the spectral index relative to the non-relativistic accretion
by increasing the energy transport to the corona. We estimate the mass
accretion rate for all the sources and find that the observed luminosity
follows a nearly linear relation with the mass accretion rate. The ratio of
X-ray luminosity from the disk to the corona increases with the mass accretion
rate. The observed $\alpha_{\text{OX}}$ shows positive and negative
correlations with luminosity. The disk-corona model explains the negative
correlation seen in the TDE sources XMMSL1J0740, XMMSL2J1446, and XMMSL1J1404.
However, TDE AT2018fyk shows a positive correlation at higher luminosity and
shows a better fit when a simple spherical adiabatic outflow model is added to
the relativistic disk-corona model. Even though the disk luminosity dominates
at a higher mass accretion rate, we show that the accretion models without a
corona are unable to explain the observations, and the presence of a corona is
essential.
