Ultra-high-time Resolution Observations of Radio Bursts on AD Leonis

TL;DR

This paper presents the highest time resolution and broadest spectral coverage observations of a stellar radio burst on AD Leonis, revealing complex structures and suggesting cyclotron maser instability as the emission mechanism.

Contribution

It provides the first high-resolution, broad-spectrum radio burst observations of AD Leonis, highlighting detailed burst structures and proposing a specific emission mechanism.

Findings

Detected a 500 mJy, 100% circularly polarized radio burst.

Observed complex spectral structures including fast-drift striae.

Suggested cyclotron maser instability as the emission process.

Abstract

We report observations of a radio burst that occurred on the flare star AD Leonis over a frequency range of 1120-1620 MHz (lambda ~18-27 cm). These observations, made by the 305m 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 ~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 implications of this possibility.