SIMULTANEOUS RAPID HARD X-RAY AND OPTICAL VARIABILITY IN AM HERCULIS - MEASUREMENT OF BLOB PARAMETERS

We describe a study of the variability observed in the Ginga hard X-ra y observation of AM Herculis. We find that the X-ray variability is be st described by shot noise, with an exponential decay time-scale of 70 s. Interpreting the shots as due to inhomogeneous accretion, we deriv e a blob length-scale of similar to 10(10) cm at the white dwarf surfa ce, a blob radius of 6 x 10(5)-4 x 10(6) cm, and a mass of similar to 10(16) g. Simultaneous optical data show for the first time a correlat ion between the hard X-ray and optical red variability, which decrease s towards bluer wavelengths. The observed correlations are explained a s occurring from bremsstrahlung and cyclotron radiation from the main shock-heated accretion region near the white dwarf surface, with the d egree of correlation decreasing towards bluer wavelengths due to the r apid decline of the cyclotron flux towards higher frequencies, and to the presence of Balmer continuum and line emission from the accretion stream in the blue bands.