Dynamic Radio Spectra from two Fireballs

TL;DR

This paper reports the first broadband VHF spectra of fireballs, revealing smooth, steep emissions possibly caused by Langmuir waves excited by electron beams, with observed frequency sweeps indicating plasma clump dynamics.

Contribution

First broadband VHF spectra of fireballs, suggesting a new emission mechanism involving Langmuir waves and plasma clumps.

Findings

Detected broadband VHF emission from fireballs between 37-54 MHz.

Observed frequency sweeps indicating plasma clump expansion.

Proposed emission mechanism involves Langmuir waves excited by electron beams.

Abstract

We present dynamic spectra from the LWA1 telescope of two large meteors (fireballs) observed to emit between 37 and 54 MHz. These spectra show the first ever recorded broadband measurements of this newly discovered VHF emission. The spectra show that the emission is smooth and steep, getting very bright at lower frequencies. We suggest that this signal is possibly emission of Langmuir waves and that these waves could be excited by a weak electron beam within the trail. The spectra of one fireball displays broadband temporal frequency sweeps. We suggest that these sweeps are evidence of individual expanding clumps of emitting plasma. While some of these proposed clumps may have formed at the very beginning of the fireball event, others must have formed seconds after the initial event.