Dynamic radio spectra from two fireballs

Abstract

We present dynamic spectra from the Long Wavelength Array 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 bump‐on‐tail instability within the trail. The spectra of one fireball display 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.

Rates, flux densities, and spectral indices of meteor radio afterglows

“…As mentioned above, of the 124 events, 4 have occurred near zenith during simultaneous beamformed observations. Analysis of the PASI images from M1 and M2 is described in Obenberger et al []. Similar to the majority of radio afterglows we observe with PASI, these events displayed a moderately fast rise and slower decay and lasted for several tens of seconds.…”

“…M2 occurred just before sunrise and therefore could not have been detected optically. M1, on the other hand, occurred at night and was confirmed by the NASA Fireball Network (http://fireballs.ndc.nasa.gov), as reported in Obenberger et al []. M3 was not detected by the Fireball Network but was confirmed with an all‐sky optical camera we operate near LWA‐SV.…”

“…The next step is to correct the beam response to the location and shapes of the meteors. Obenberger et al [] described a process where the beam contribution to the spectra was removed for both M1 and M2. This model assumed that the meteor trails were much longer than the width of the beam and uniform in brightness and used PASI to find the distance away from the beam center.…”

“…The measurements from Obenberger et al [] were made using two tunings, one centered at 45.45 MHz and the other at 65.05 MHz. The upper tunings of each observation were rendered unusable because the beamformer did not have enough dynamic range to properly record the extremely bright forward scatter of analog TV channels.…”

“…Obenberger et al [] did not include a power law fit for the spectra of the two radio afterglows. This analysis was excluded from the paper because the spectrum of M1 and the second meteor (M2) contained several effects that made comparison difficult.…”