X-Ray Emission Produced by a Relativistic Beam of Runaway Electrons
Accelerated by Quasi-Electrostatic Thundercloud Fields
N. G. Lehtinen, M. Walt, U. S. Inan, T. F. Bell, V. P. Pasko
In an experiment described by Fishman et al.
(1994), high energy
photons of atmospheric origin
were detected by the Burst and Transient Source
Experiment (BATSE) detectors, located on the Compton Gamma Ray
Observatory (CGRO). In this paper we assess the possibility that the
bursts may be bremsstrahlung produced by relativistic (> 1 MeV) runaway
electron beams accelerated in an avalanche process by quasi-static
thundercloud fields. We consider the height-dependent density profile
of the relativistic electrons specified as a function of time in the
context of a previously reported runaway model (Bell et al., 1995).
The electron beam is modeled as
a vertical cylinder with radius 10 km, and numerical estimates are
provided of x-ray fluxes which would be observed at the
The predicted x-ray fluxes at the satellite altitude and
at horizontal distances of up to 500 km from the source are found to be
comparable to the experimental data.
STAR Laboratory, Stanford University, Stanford, CA 94305
Figure. The photon fluence (flux integrated over
time in the impulse) as a function of the initial thundercloud charge,
found for BATSE energy ranges at the point exactly above the source.
(satellite height is 500 km)
Bell, T. F., V. P. Pasko, and U. S. Inan, Runaway electrons
as a source of Red Sprites in the
mesosphere, Geophys. Res. Lett., 22, 2127, 1995.
Fishman G. J. et al., Discovery of Intense Gamma-Ray Flashes of
Atmospheric Origin, Science, 264, 1313, 1994.