  We present RHESSI and TRACE observations of multiple flare activity that
occurred in the active region NOAA 10656 over the period of two hours on 2004
August 18. Out of four successive flares, there were three events of class C
while the final event was a major X1.8 solar eruptive flare. The events during
the pre-eruption phase, i.e., before the X1.8 flare, are characterized by
localized episodes of energy release occurring in the vicinity of an active
region filament which produced intense heating along with non-thermal emission.
A few minutes before the eruption, the filament undergoes an activation phase
during which it slowly rises with a speed of ~12 km/s. The filament eruption is
accompanied with an X1.8 flare during which multiple HXR bursts are observed up
to 100-300 keV energies. We observe a bright and elongated coronal structure
simultaneously in E(UV) and 50-100 keV HXR images underneath the expanding
filament during the period of HXR bursts which provides strong evidence for
ongoing magnetic reconnection. This phase is accompanied with very high plasma
temperatures of ~31 MK and followed by the detachment of the prominence from
the solar source region. From the location, timing, strength, and spectrum of
HXR emission, we conclude that the prominence eruption is driven by the
distinct events of magnetic reconnection occurring in a current sheet formed
below the erupting filament. These multi-wavelength observations also suggest
that the localized magnetic reconnections associated with different
evolutionary stages of the filament in the pre-eruption phase play a crucial
role in destabilizing the filament by a tether-cutting process leading to
large-scale eruption and X-class flare.
