Non‐stormtime injection of energetic particles into the slot‐region between Earth's inner and outer electron radiation belts as observed by STSAT‐1 and NOAA‐POES

The slot‐region between Earth's inner and outer electron radiation belts was observed on 24 February 2004 by the satellite STSAT‐1 to be populated by quasi‐trapped electrons of energy 100‐400 keV. This injection lasted for several hours and took place during a non‐stormtime substorm. This appears to be the first observation of a slot‐region electron injection that did not occur during a geomagnetic storm. We also report multi‐instrument observations of this event from NOAA‐POES and CPMN magnetic observatories, and we consider physical mechanisms that may account for the phenomenon.