  Off-limb observations of the solar corona after Coronal Mass Ejections (CMEs)
often show strong, compact, and persistent UV sources behind the eruption. They
are primarily observed by the SOHO/UVCS instrument in the "hot" Fe XVIII
{\lambda}974 {\AA} line and are usually interpreted as a signature of plasma
heating due to magnetic reconnection in the post-CME Current Sheet (CS).
Nevertheless, the physical process itself and the altitude of the main energy
release are currently not fully understood. In this work, we studied the
evolution of plasma heating after the CME of 2004 July 28 by comparing UV
spectra acquired by UVCS with soft X-ray (SXR) and hard X-ray (HXR)images of
the post-flare loops taken by GOES/SXI and RHESSI. The X-ray data show a
long-lasting extended source that is rising upwards, toward the
high-temperature source detected by UVCS. UVCS data show the presence of
significant non-thermal broadening in the CS (signature of turbulent motions)
and a strong density gradient across the CS region. The thermal energy released
in the HXR source is on the order of about 10^32 erg, a factor about 2-5 larger
than the energy required to explain the high-temperature plasma sampled by
UVCS. Nevertheless, the very different time evolutions of SXR and HXR sources
compared to the UV emission suggest that reconnection occurring above the
post-eruption arcades are not directly responsible for the high-temperature
plasma sampled higher up by UVCS. We conclude that an additional plasma heating
mechanism (such as turbulent reconnection) in the CS is likely required.

Solar and Stellar Astrophysics