The relativistic solar particle event on 28 October 2021: Evidence of particle acceleration within and escape from the solar corona

Aims. We analyse particle, radio, and X-ray observations during the first relativistic proton event of solar cycle 25 detected on Earth. The aim is to gain insight into relationship between particles in space processes acceleration propagation eruptive events. Methods. To this end, we used ground-based neutron monitor measurements nucleons space-borne electrons with similar speed determine arrival times at 1 AU infer their release times. compared time histories non-thermal atmosphere escape interplanetary space, as traced by radio spectra light curves images. Results. Non-thermal corona are found be accelerated different regions. Some confined closed magnetic structures expanding course event. Three episodes electron revealed groups decametric-to-kilometric type III bursts. group appears low-frequency side a II burst produced coronal shock wave. two latter accompanied higher frequencies bursts rapid drifts both lower (forward- or reverse-drifting bursts). They beams that propagate sunward anti-sunward. observed near Earth released third bursts, more than ten minutes after signatures formation wave corona. Although active region central meridian, several tens degrees east footpoint nominal Parker spiral Earth, kilometric spectrum situ detection Langmuir waves demonstrate direct connection L1 Lagrange point field lines onto which Sun. Conclusions. interpret forward- evidence reconnection an erupting flux rope ambient open lines. discuss origin across scenarios: (1) CME-driven it intercepts rooted western hemisphere (2) alternative where initially fields get access through these