Study of Rapid Variability in CYGNUS-X-1

Abstract

The EXOSAT Medium Energy instrument has been used with the new HER6 mode to study the rapid variability of Cygnus X-1. It was found that the fluctuations in the higher energy band (5 - 14 keV) lagged behind those in the lower band (2 - 5 keV) by about 6 milliseconds. This confirms predictions of the inverse Compton model and gives an upper limit to the scale-size of the hot gas clouds.