Time lags in Narrow-line Seyfert 1 galaxies and the origin of their soft excess emission

The origin of soft X-ray excess emission from type 1 active galactic nuclei has remained a major problem for the last two decades. It has not been possible to distinguish alternative models for the soft excess emission despite the excellent data quality provided by XMM-Newton and Chandra. Here we present observations of time lags between the soft and hard band X-ray emission and discuss the implications to the models for the soft excess. We also device a method to distinguish the models for the soft excess using Suzaku's broadband capability.