  We study the magnetic field structures of hard X-ray sources and flare
ribbons of the M1.1 flare in active region NOAA 10767 on 2005 May 27. We have
found in a nonlinear force-free field extrapolation, over the same polarity
inversion line, a small pre-eruptive magnetic flux rope located next to sheared
magnetic arcades. Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and
Transition Region and Coronal Explorer (TRACE) observed this confined flare in
the X-ray bands and ultraviolet (UV) 1600 \AA \ bands, respectively. In this
event magnetic reconnection occurred at several locations. It first started at
the location of the pre-eruptive flux rope. Then, the observations indicate
that magnetic reconnection occurred between the pre-eruptive magnetic flux rope
and the sheared magnetic arcades more than 10 minutes before the flare peak. It
implied the formation of the larger flux rope, as observed with TRACE. Next,
hard X-ray (HXR) sources appeared at the footpoints of this larger flux rope at
the peak of the flare. The associated high-energy particles may have been
accelerated below the flux rope, in or around a reconnection region. Still, the
close spatial association between the HXR sources and the flux rope footpoints
favors an acceleration within the flux rope. Finally, a topological analysis of
a large solar region including the active regions NOAA 10766 and 10767 shows
the existence of large-scale Quasi-Separatrix Layers (QSLs) before the eruption
of the flux rope. No enhanced emission was found at these QSLs during the
flare, but the UV flare ribbons stopped at the border of the closest
large-scale QSL.
