The X17.2 flare occurred in NOAA 10486: an example of filament destabilization caused by a domino effect

Context. It is now possible to distinguish between two main models describing the mechanisms responsible for eruptive flares : thestandard model, which assumes that most of the energy is released, by magnetic reconnection, in the region hosting the core of asheared magnetic field, and the breakout model, which assumes reconnection occurs at first in a magnetic arcade overlaying theeruptive features.Aims. We analyze the phenomena observed in NOAA 10486 before and during an X17.2 flare that occurred on 2003 October 28,to study the relationship between the pre-flare and flare phases and determine which model is the most suitable for interpreting thisevent.Methods. We performed an analysis of multiwavelength data set available for the event using radio data (0.8–4.5 GHz), images inthe visible range (WL and Hα), EUV images (1600 and 195 Å), and X-ray data, as well as MDI longitudinal magnetograms. Wedetermined the temporal sequence of events occurring before and during the X17.2 flare and the magnetic field configuration in thelinear force-free field approximation.Results. The active region was characterized by a multiple arcade configuration and the X17.2 flare was preceded, by ∼2 h, by thepartial eruption of one filament. This eruption caused reconnection at null points located in the low atmosphere and a decrease inmagnetic tension in the coronal field lines overlaying other filaments present in the active region. As a consequence, these filamentswere destabilized and the X17.2 flare occurred.Conclusions. The phenomena observed in NOAA 10486 before and during the X17.2 flare cannot be explained by a simple scenariosuch as the standard or breakout model, but instead in terms of a so-called domino effect, involving a sequence of destabilizingprocesses that triggered the flare.