Reverberation mapping analysis of the broad-line region in Seyfert galaxy NGC 4151

Using the optical data of the 1993 international watch of NGC 5141, we made follow-up reverberation mapping analyses of its broad line region (BLR). W e found the transfer function of the BLR for the 1993 data is entirely diff erent from that for the 1988 international watch. We conclude that the stru cture of the BLR had changed in those 5 years and it is this change in stru cture that is responsible for the very different sizes of the BLR deduced f rom the two sets of data.