The energy distribution of the electron precipitation responsible for extremely narrow (70 m) and dynamic auroral filaments is found to be sharply peaked at around 8 keV. The events were captured with high resolution low-light optical imagers located near Tromsø, Norway. The method uses imaging in two emissions which have different energy dependent responses to auroral electron precipitation. The key feature of the events was that no difference in the altitude of the two emissions was detected, nor any time-of-flight dispersion, thus leading to the conclusion that the filaments were caused by monoenergetic precipitation. Comparisons with an electron transport and ion chemistry model show that the high energy filaments were embedded in a region of lower energy precipitation of about 4 keV. There is currently no consistent theory to explain the characteristics of the observed auroral structures.