X-ray and optical flickering in EF Eri.

Abstract

A study of the short-time-scale variability of the polar system EF Eri is presented based on simultaneous hard and soft X-ray monitoring with the Exosat Observatory and optical photometry from CTIO. The observations are used to investigate the nature of the flickering in this system, and the correlations between the variability in the three bands. The hard X-ray flickering is characterized by a quasi-periodic 10-percent modulation at about 230 sec. The soft X-ray and optical flickering have higher amplitudes but, in contrast, lack any dominant time-scales. A significant degree of correlation exists between the flickering in all three bands. The correlation between the hard X-ray and optical flickering is very strong, while that between the hard and soft X-rays is much lower. The implications of these results for the origin of the different spectral components, and the constraints that they place on models of the polecap emission region, are discussed.