An M1.5 Flare Triggered by a Multireconnection Process

We studied the magnetic configuration of active region NOAA 10672, where two different mechanisms seem to contribute to its instability, to the subsequent M1.5 flare, and to a halo CME. The analysis of full-disk SOHO/MDI magnetograms and of WL and 171 A TRACE images shows in fact that both flux emergence and horizontal displacements of photospheric flux concentrations have a key role in triggering the event. On the basis of these pre-flare mechanisms, we provide a description of a multireconnection process able to explain the flare evolution observed by TRACE, as well as the two-step profile in X-ray emission observed in the 1 – 8 A band. Moreover, this work highlights some photospheric signatures that can be considered as flare precursors.