  We discover an unidentified strong emission feature in the X-ray spectrum of
EXO 1745$-$248 obtained by RXTE at 40 hr after the peak of a superburst. The
structure was centered at 6.6 keV and significantly broadened with a large
equivalent width of 4.3 keV, corresponding to a line photon flux of 4.7
$\times$ 10$^{-3}$ ph cm$^{-2}$ s$^{-1}$. The 3-20 keV spectrum was reproduced
successfully by a power law continuum with narrow and broad (2.7 keV in FWHM)
Gaussian emission components. Alternatively, the feature can be described by
four narrow Gaussians, centered at 5.5 keV, 6.5 keV, 7.5 keV and 8.6 keV.
Considering the strength and shape of the feature, it is unlikely to have
originated from reflection of the continuum X-rays by some optically thick
materials, such as an accretion disk. Moreover, the intensity of the emission
structure decreased significantly with an exponential time scale of 1 hr. The
feature was not detected in an INTEGRAL observation performed 10 h before the
RXTE observation with a line flux upper limit of 1.5 $\times$ 10$^{-3}$ ph
cm$^{-2}$ s$^{-1}$. The observed emission structure is consistent with
gravitationally redshifted charge exchange emission from Ti, Cr, Fe, and Co. We
suggest that the emission results from a charge exchange interaction between a
highly metal-enriched fall back ionized burst wind and an accretion disk, at a
distance of $\sim$60 km from the neutron star. If this interpretation is
correct, the results provide new information on the understanding of nuclear
burning processes during thermonuclear X-ray bursts.

High Energy Astrophysical Phenomena