  Extreme ultraviolet (EUV) waves are thought to be the propagating footprint
of the shock on the solar surface. One of the key questions in SEP research is
the timing of the SEP release with respect to the time when the EUV wave
magnetically connects with an observer. Taking advantage of close-to-the-Sun
measurements by Parker Solar Probe (PSP) and Solar Orbiter (SolO), we
investigate an SEP event that occurred on 2021 September 28 and was observed at
different locations by SolO, PSP, STEREO-A, and near-Earth spacecraft. During
this time, SolO, PSP and STEREO-A shared similar nominal magnetic footpoints
relative to the SEP source region but were at different heliocentric distances.
We find that the SEP release times estimated at these four locations were
delayed compared to the times when the EUV wave intercepted the footpoints of
the nominal magnetic fields connecting to each spacecraft by around 30 to 60
minutes. Combining observations in multiple wavelengths of radio, white-light,
and EUV, with a geometrical shock model, we analyze the associated shock
properties, and discuss the acceleration and delayed release processes of SEPs
in this event as well as the accuracy and limitations of using EUV waves to
determine the SEP acceleration and release times.
