Deep HMI magnetogram of 160 summed-up, de-rotated individual magnetograms between 09:00 and 11:00 UT on 2016 July 3. The magnetogram is clipped between ±100 G to enhance weak magnetic fields. The filled red contour corresponds to the filament in Hα at rest extracted from a ChroTel filtergram before the eruption at 09:39 UT. The yellow and orange lines represent the two slit positions of the spectrograph at about 10:06 UT and 10:09 UT, corresponding to maps A–C.