Upper panel: the intensity-time history of the precursor event and the main event at ACE, seen in the four deflected electron channels on EPAM. The energies of the channels are 38–53 keV (red), 53–103 keV (green), 103–175 keV (blue) and 175–315 keV (cyan) and they are plotted as 5 min averages and spin averages. The dashed line indicates the possible velocity dispersion seen before the main onset at around 13:50 UT. Lower panels: the magnetic field at ACE, plotted as the magnitude (B), colatitude (theta) and azimuth (phi).