We have identified for the first time an energy-time dispersion of
precipitating electron flux in a pulsating aurora patch, ranging from
6.7 keV to 580 keV, through simultaneous in-situ observations of
sub-relativistic electrons of microburst precipitations and lower-energy
electrons using the LAMP sounding rocket launched from the Poker Flat
Research Range in Alaska. Our observations reveal that precipitating
electrons with energies of 180-320 keV were observed first, followed by
250-580 keV electrons 0-30 ms later, and finally, after 500-1000 ms,
6.7-14.6 keV electrons were observed. The identified energy-time
dispersion is consistent with the theoretical estimation that the
relativistic electron microbursts are a high-energy tail of pulsating
aurora electrons, which are caused by chorus waves propagating along the
field line.