Large-scale magnetic overview of the flaring region. Top panel is the radial magnetic field map of the full Sun in Carrington longitude and latitude coordinate system (saturated to ±100 G). The black rectangle identifies the active region in which the flare was triggered. The lower panel shows the signed-log (slog) of the magnetic squashing factor, Q. In the inset the latitude and longitude positions of the three magnetic nulls are marked with red circles. The black cross-hair is roughly at the same location as that in Fig. A.5A. The red arrows point to the locations of remote brightenings (as those marked in Fig. A.5).