The soft X-ray variability of NGC 5548.

Abstract

The soft X-ray variability of NGC 5548 is studied using EXOSAT's low energy telescope in conjunction with the channel multiplyer array (CMA). For the first time, the pulse height distribution of the CMA data is used to infer information on the spectral variability. The spectrum of NGC 5548 consists of a hard power law and a soft component. During a one day observation in 1986 a considerable softening of the soft component flux was observed while the power law brightened only slightly. Significant changes in the properties of the soft X-ray emitting region or in a warm absorbing medium may explain the spectral softening.