Analysis and interpretation of a fast limb CME with eruptive prominence, C-flare and EUV dimming

Aims. Coronal mass ejections or CMEs are large dynamical solar-corona events. The mass balance and kinematics of a fast limb CME, including its prominence progenitor and the associated flare, will be compared with computed magnetic structures to look for their origin and effect. Methods. Multi-wavelength ground-based and spaceborne observations are used to study a fast W-limb CME event of December 2, 2003, taking into account both on and off disk observations. Its erupting prominence is measured at high cadence with the Pic du Midi full Hα line-flux imaging coronagraph. EUV images from SOHO/EIT and CORONAS-F/SPIRIT space instruments are processed including difference imaging. SOHO/LASCO images are used to study the mass excess and motions. Computed coronal structures from extrapolated surface magnetic fields are compared to observations. Results. A fast bright expanding coronal loop is identified in the region recorded slightly later by GOES as a C7.2 flare, followed by a brightening and an acceleration phase of the erupting material with both cool and hot components. The total coronal radiative flux dropped by ∼ 7% in the 19.5 nm channel and by 4% in the 17.5 nm channel, revealing a large dimming effect at and above the limb over a 2 hour interval. The typical 3-part structure observed 1 hour later by the Lasco C2 and C3 coronagraphs shows a core shaped similarly to the eruptive filament/prominence. The total measured mass of the escaping CME (∼ 1.5 · 1016 g from C2 LASCO observations) definitely exceeds the estimated mass of the escaping cool prominence material although assumptions made to analyze the Hα erupting prominence, as well as the corresponding EUV darkening of the filament observed several days before, made this evaluation uncertain by a factor of 2. This mass budget suggests that the event is not confined to the eruption region alone. From the current free extrapolation we discuss the shape of the magnetic neutral surface and a possible scenario leading to an instability, including the small scale dynamics inside and around the filament.