We report observations of a radio burst that occurred on the flare star AD Leonis over a frequency range of 1120-1620 MHz ( \lambda \approx 18–27 cm ) .
These observations , made by the 305 m telescope of the Arecibo Observatory , are unique in providing the highest time resolution ( 1 ms ) and broadest spectral coverage ( \Delta \nu / \nu = 0.36 ) of a stellar radio burst yet obtained .
The burst was observed on 2005 April 9 .
It produced a peak flux density of \sim 500 mJy and it was essentially 100 % right-circularly polarized .
The dynamic spectrum shows a rich variety of structure : patchy emission , diffuse bands , and narrowband , fast-drift striae .
Focusing our attention on the fast-drift striae , we consider the possible role of dispersion and find that it requires rather special conditions in the source to be a significant factor .
We suggest that the emission may be due to the cyclotron maser instability , a mechanism known to occur in planetary magnetospheres .
We briefly explore possible implications of this possibility .