  We study the evolution of a group of TRACE 195 A coronal loops overlying a
reverse S-shaped filament on 2001 June 15. These loops were initially pushed
upward with the filament ascending and kinking slowly, but as soon as the
filament rose explosively, they began to contract at a speed of ~100 km/s, and
sustained for at least 12 min, presumably due to the reduced magnetic pressure
underneath with the filament escaping. Despite the contraction following the
expansion, the loops of interest remained largely intact during the filament
eruption, rather than formed via reconnection. These contracting loops
naturally formed a shrinking trap, in which hot electrons of several keV, in an
order of magnitude estimation, can be accelerated to nonthermal energies. A
single hard X-ray burst, with no corresponding rise in GOES soft X-ray flux,
was recorded by the Hard X-ray Telescope (HXT) on board Yohkoh, when the
contracting loops expectedly approached the post-flare arcade originating from
the filament eruption. HXT images reveal a coronal source distinctly above the
top of the soft X-ray arcade by ~15". The injecting electron population for the
coronal source (thin target) is hardening by ~1.5 powers relative to the
footpoint emission (thick target), which is consistent with electron trapping
in the weak diffusion limit. Although we can not rule out additional
reconnection, observational evidences suggest that the shrinking coronal trap
may play a significant role in the observed nonthermal hard X-ray emission
during the flare decay phase.
