a) Image in the continuum acquired at BBSO at 17:49:52 UT on 28 February 1999, the arrow indicates a sunspot with a δ-configuration; b) High resolution H_α image acquired at BBSO at 17:49:48 UT, showing several filaments; the arrows indicate two filaments involved in the flaring process; c) Magnetogram acquired at BBSO, showing the magnetic configuration of the active region at 17:49:52 UT; the blue and green contours indicate the negative and positive magnetic field at  ± 200 (solid line),  ± 1000 G (dashed line). The circle indicates the location of the δ spot. The images have a field of view of 161 × 61 Mm².