Overview of the selected fixed sources for the 2021 October 9 event. (a) Solar flare source. The panel shows the smoothed GONG zero-point-corrected magnetogram for 2021-10-09 at 06:04 UT (saturated at ±50 G), the PFSS-derived location of the heliospheric current sheet at 2.5 R_⊙ (lime contour), the mapping of AR 12882 onto the 2.5 R_⊙ PFSS source surface (red contour), and the selected fixed-source area to employ for SEP injection (yellow contour). (b) Coronal shock source. The panel shows the solar wind radial speed at the Enlil inner boundary of 21.5 R_⊙ at the point of maximum width of the CME insertion (2021-10-09 at 15:39 UT, same as Fig. 3a), the location of the modelled heliospheric current sheet (black contour), the selected fixed-source area to employ for SEP injection (white contour), and the projected Enlil-modelled field lines connecting each of the five observers to the 21.5 R_⊙ sphere.