Hard X-ray observations of white dwarf binary systems

THE ability of degenerate dwarfs, as opposed to neutron stars, to radiate at X-ray wavelengths has created much theoretical interest. Ariel 5 hard X-ray observations indicate that current theories seem inadequate to explain all aspects of the observations. Using the Imperial College hard X-ray scintillation telescope (ST) on Ariel 5, several short period (up to 12 h) binary star systems have been studied and are described here. This study was carried out after a very hard X-ray flux was detected from AM Herculis leading to a search for similar signals from optically similar star systems. The detector used consists of 8 cm² of Csl crystal actively collimated to 8° FWHM and covers the energy range 26-1,200 keV. It is offset from the satellite spin axis, thereby enabling background subtraction using a modulation technique. The instrument and its operation are described fully elsewhere¹.