  The current sheet is an essential feature in solar flares and is the primary
site for magnetic reconnetion and energy release. Imaging observations feature
a long linear structure above the candle-flame-shaped flare loops, which
resembles the standard flare model with the current sheet viewed edge-on. We
investigate the thermal properties of plasmas surrounding the linear sheet
during flares, using EUV observations from the Atmospheric Imaging Assembly
(AIA) onboard the Solar Dynamics Observatory (SDO). The differential emission
measure (DEM) analyses show evidence of high temperatures in the plasma sheets
(PSs), containing hot emissions from only a narrow temperature range,
suggestive of an isothermal feature. The sheet's temperature remains constant
at different heights above the flare arcade, peaking at around logT=7.0-7.1;
while the well-studied 2017 September 10 X8.2 flare exhibits as an exception in
that the temperature decreases with an increasing height and peaks higher
(logT=7.25) during the gradual phase. Most PS cases also hold similar emission
measures and thicknesses; while the PS's emissions drop exponentially above the
flare arcade, the sheet thicknesses show no significant height association as
for all the measurements. The characteristics of isothermal and steady
temperature suggests balanced heating and cooling processes along the current
sheet, particularly additional heating may exist to compensate for the
conductive and radiative cooling away from the reconenction site. Our results
suggest a steady and uniform sheet structure in the macroscopic scale that
results from flare reconnection.
