Rapid aperiodic pulsing (quasi- periodic oscillations; QPO's) in low-mass X-ray binaries is probably due to interactions between the circulating matter in the accretion disk and the magnetosphere of the neutron star. These pulsations are directly seen with the Ginga satellite during a burst from the "Rapid Burster" source. The mechanism that gives rise to QPO pulsations is not yet known. They may be symptomatic of a heretofore undetected pulsar spinning almost 1000 times a second.
Spectral features found at relatively high X-ray energies are believed to be due to electrons spiraling in the very high magnetic field of neutron stars. The absorption feature in the spectra of the X-ray pulsar 1538-52 observed by Ginga is seen to vary with the (numbered) phase of the pulsing. This cyclotron radiation is a direct diagnostic of the hot plasmas and strong magnetic fields in the polar regions of the neutron star.
The cross correlation of the X-ray and optical fluxes of BY Cam show the rapid flickering in both bands to be highly correlated on ~1 minute time scales. BY Cam (=H0538+608) is a magnetic white-dwarf cataclysmic-variable system (AM Her type). The radiation may originate in a shock front just above the white-dwarf surface. This detection required the large apertures of the Ginga satellite and simultaneous optical and X-ray observations (Silber et al 1992, ApJ, 389, 704).
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