GECAM discovery of peculiar oscillating particle precipitation events

Charged particle precipitation typically manifests as a gradual increase and decrease of flux observed by space detectors.Cases with rapid flux variation are very rare, while periodic events are even more extraordinary.These oscillating particle precipitation (OPP) events are usually attributed to the bounce motion of electrons probably induced by lightning.However, the origin of these oscillation events is still on debate.Here we report three peculiar charged particle precipitation events detected by GECAM during a geomagnetic storm on March 21, 2024, with two exhibiting significant periodicity. These events were observed around the same region during three consecutive orbits with a life time of more than 3.5 h.Through comprehensive temporal and spectral analyses, we find that one of the OPP events exhibited a transition in spectral lag of mini-pulses, shifting from “softer-earlier" to “softer-later" while showing no significant time evolution in overall frequency characteristics, and that there is no association found between these two OPP events and lightning activity nearby.Finally, we discussed possible scenarios to explain these GECAM-detected OPP events,and we found that they may represent a new type of particle precipitation event or a peculiar lightning-induced electron precipitation (LEP).