We study brightness, volume and heights of the
X-ray thermal emission components for an M-class solar
flare on 17 May 2012. Based on the RHESSI data availabil-
ity, we present the results for 01:42–01:58 UT over the late-
flare phase. It is observed that the spatial evolution of the
thermal emission components 6–12 and 12–18 keV are well
associated with the hottest plasma in the corona. Results
show that the ascending height (∼1.35 × 10 4 km) and speed
(∼14.0 km s −1 ) of coronal source component 6–12 keV is
slightly smaller than the ascending height (∼1.45 × 10 4 km)
and speed (∼15.1 km s −1 ) of the coronal source component
12–18 keV. Mean flux intensity (I mean ) of the 6–12 keV
maintained a good fit (χ 2 = 0.41) with the correspond-
ing volume (V ) following strongly the power law [I mean =
(15.8 ± 0.21)V −1.28±0.03 ]. In contrast, the 12–18 keV main-
tained a weak fit (χ 2 = 2.37) following still the power law
[I mean = (0.19 ± 0.01)V −1.88±0.16 ]. The power law indices
(−1.28 ± 0.03; −1.88 ± 0.16) obtained by the observational
analysis slightly differ from the power law index (−1.67)
obtained by a theoretical model. The observations are con-
sistent with adiabatic expansion of the coronal source com-
ponent.

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• On the time evolution of brightness, volume and height of a coronal source in an M-class flare