First detection of a terrestrial MeV X‐ray burst

Abstract

Abstract. We report the fixst detection of a terrestrial X-ray burst extending up to MeV energies, made by a liquid-nitrogen-cooled germanium detector (~ 2 keV FWHM resolution) on a high-altitude balloon at 65.5 ø magnetic latitude (L=5.7) in the late afternoon (1815 MLT) during low geomagnetic activity. The burst occurred at 1532-1554 UT on August 20, 1996, and consisted of seven peaks of -60-90 s duration, spaced by ~100-200 s, with quasi-periodic (~10-20 s) modulation of the peak count rates. The very hard X-ray spectrum extends to the instrumental limit of 1.4 MeV, and is consistent with bremsstrahlung emission from monoenergetic, ~1.7 MeV, precipitating electrons. Since the trapped relativistic electrons showed a steeply falling energy spectrum from 0.6 to 4 MeV (at L=6.6), the precipitation mechanism appears to be highly energy selective. The modulation frequencies suggest scattering of the MeV electrons due to gyro-resonance with Doppler-shifted electromagnetic ion cyclotron waves, but either equatorial proton densities a factor of ~102 higher than typical for the plasmasphere or significant O + densities would be Here we present high spectral resolution balloon observations of the most energetic terrestrial hard X-ray burst ever detected. The nearly stationary balloon platform allows the temporal evolution of the entire precipitation event to be observed.

The Upgraded CARISMA Magnetometer Array in the THEMIS Era

“…The results of their analysis are consistent with the theoretical study of Summers and Thorne (2003). It has also been inferred from balloon observations of X-ray emissions in the dusk sector that EMIC waves can cause precipitation of MeV energy electrons (Foat et al 1998;Millan et al 2002) usually during storm recovery phase.…”

Review of radiation belt relativistic electron losses

“…The precipitating electron energy spectrum was very hard with e-folding energies in excess of 500 keV. Balloon observations of relativistic precipitation occurring at dusk have also been reported, and indicate that duskside REP is a distinct class of precipitation (Foat et al, 1998;Lorentzen et al, 2000;Millan et al, 2002).…”

The Balloon Array for RBSP Relativistic Electron Losses (BARREL)

“…1 which shows an example of duskside precipitation measured by the MAXIS balloon payload. Pitch-angle scattering by electromagnetic ion cyclotron (EMIC) waves, proposed much earlier on theoretical grounds (Thorne and Kennel 1971), may be the precipitation mechanisms (e.g., Foat et al 1998;Lorentzen et al 2000). However, this hypothesis is based primarily on the duskside location, and simultaneous measurements of the waves and precipitation have so far not been available to test it.…”

“…The conversion between the spectrum of counts observed in balloon-borne X-ray detectors and the spectrum of electrons incident on the atmosphere is a well-established one, and not a new development (e.g., Berger and Seltzer 1972;Foat et al 1998). Nonetheless, we describe it here because it is the primary BARREL measurement.…”