Observation and interpretation of Leonid impact flashes on the Moon in 2001

We present observations of lunar Leonid impact ashes recorded in 2001 November from Spain. Four impact ashes were detected on November 18. Another ash was also recorded on the same night, which appears to be impact related, and two more on that night are possibly, but not unambiguously, of impact nature. On November 19 another ash was detected, which very likely resulted from an impact. The brightest impact ash reached a peak brightness of 5.2 +/- 0.3 mag in V; it had a very dim precursor just 0.02 s prior to peak brightness and had a very long lasting afterglow that remained visible for more than 600 ms with oscillations in brightness; this unique and unexpected behavior challenges current models of impact ashes. The other ashes did not show such a behavior and remained visible for a few tens of milliseconds. Adopting the luminous efficiency derived for the 1999 lunar Leonids (2 x 10(3)), our observations can be used to estimate meteoroid fluxes. The observations are compatible with a flux of 0.1 meteoroids of mass larger than 2 x 10(-8) kg km(-2) hr(-1) on November 18 at 18:15 UT, provided that a mass index of 1.69 is used. Both the flux and the mass index agree with meteor observations carried out in 2001 from several locations on Earth.