Pinhole x-ray cameras for imaging small-scaled auroral structures

A balloon-borne x-ray pinhole camera has been developed to detect and image auroral x-rays in the energy range 20 to 120 keV. The authors have flown this camera on four different occasions and have imaged bremsstrahlung x-rays from precipitated energetic electrons in the auroral zone and from a circumpolar navigating balloon in Antarctica. The images, which include several dynamic precipitation temporal forms, show that auroral x-rays persistently include small spatial structures of ∼20 km (at ionospheric heights). The x-ray energy spectral information as a function of space and time shows that electron precipitation often includes two energy components that can be fit by exponential functions. Typical e-folding energies of these spectra are a few kilo-electron-volts and several tens of kilo-electron-volts. The x-ray camera remote senses characteristics of energetic electron sources in the distant magnetosphere that cannot be achieved by any other means