Enigma of a flare involving multiple-loop interactions: Emerging, colliding loops or magnetic breakout?

We present observations of a C9.4 flare on 2002 June 2 in EUV (TRACE), X-rays (RHESSI), and H alpha (Meudon and Ondrejov) showing evidence for multiple-loop interactions as the cause of the flare. The multiwavelength data reveal some striking phenomena that can be used to test different models for solar eruptive events: (1) involvement of a quadrupolar magnetic configuration; (2) loop expansion and ribbon motion in the preimpulsive phase; (3) gradual formation of a new compact loop with a long cusp at the top during the impulsive phase of the flare; (4) appearance of a large, twisted loop above the cusp expanding outward immediately after the hard X-ray peak; (5) eruption of an S-shaped preflare filament trailing closely behind the twisted loop; and (6) X-ray emission observed only from the new compact loop and the cusp. The emerging flux model and the magnetic breakout model are both applied to interpret the observations. We find that both models are able to explain the general change of the loop morphology for the flare. The magnetic breakout model best addresses the preimpulsive features. Most > 25 keV hard X-rays were emitted during the formation process of the EUV cusp, suggesting that fast reconnection occurred during the restructuring of the magnetic configuration, resulting in more efficient particle acceleration, while the reconnection slowed after the cusp was completely formed and the magnetic geometry was stabilized.