Heliocentric positions and nominal Parker spiral magnetic connections of the spacecraft during the 2021 April 17 SEP event at 16:20 UT. Earth, PSP, SolO, and STA are marked by green, purple, sky-blue, and red stars, respectively. The spiral curves are calculated from the event-time solar wind speeds, and the arrow indicates the radial direction from the flare site. The gray sector denotes the assumed longitudinal extent of the source region.