Observed X‐rays associated with kilometric continuum

Abstract

Kilometric continuum (KC) is a recently identified nonthermal magnetospheric radio/plasma wave phenomenon that consists of many narrowband emission lines of nearly constant frequency. The temporal structures of the KC wave intensities measured from the Geotail satellite in near equatorial positions at geocentric distances of 9–30 Earth radii were, on several occasions, similar to the temporal structures of X‐rays simultaneously emitted from the atmosphere and mapped in position from the Polar satellite at lower altitudes and at high latitudes. The similarity in behavior of KC waves and X‐rays might result from the fact that bremsstrahlung X‐rays can be generated in the atmosphere by precipitating electrons produced at high altitudes by incident KC waves. KC waves at low latitudes appear correlated with X‐rays at high latitudes. Our study supports the premise that KC waves interacting with high‐altitude energetic electrons can lead to the production of X‐rays at low altitudes from the resultant precipitation of the electrons. Thus the Polar and Geotail satellites may be used to map the spatial spread of KC, a feat that cannot be currently accomplished with waves observed from a single satellite. In this investigation, it is found that the X‐ray emissions extend over a wide range of latitudes and may span a broad longitudinal interval. The energy spectra of X‐rays emitted from the Earth at the times of KC events have been examined and found to display a wide variety of intensities and spectral shapes as do the spectra of X‐rays associated with auroral kilometric radiation (AKR) events. For most of the high‐latitude satellite passes when KC but no AKR was present, the X‐ray energy spectra were harder than at times associated with AKR.