  The spatial and spectral properties of three solar flare coronal X-ray loops
are studied before, during and after the peak X-ray emission. Using
observations from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI),
we deduce the temporal changes in emitting X-ray length, corpulence, volume,
position, number density and thermal pressure. We observe a decrease in the
loop length, width and volume before the X-ray peak, and an increasing number
density and thermal pressure. After the X-ray peak, volume increases and loop
corpulence grows due to an increasing width. The volume variations are more
pronounced than the position variations, often known as magnetic line
contraction. We believe this is the first dedicated study of the temporal
evolution of X-ray loop lengths and widths. Collectively, the observations also
show for the first time three temporal phases given by peaks in temperature,
X-ray emission and thermal pressure, with minimum volume coinciding with the
X-ray peak. Although the volume of the flaring plasma decreases before the peak
in X-ray emission, the relationship between temperature and volume does not
support simple compressive heating in a collapsing magnetic trap model. Within
a low beta plasma, shrinking loop widths perpendicular to the guiding field can
be explained by squeezing the magnetic field threading the region. Plasma
heating leads to chromospheric evaporation and growing number density,
producing increasing thermal pressure and decreasing loop lengths as electrons
interact at shorter distances and we believe after the X-ray peak, the
increasing loop corpulence.
