THE SEYFERT-GALAXY NGC-4151 - PEAK ACTIVITY ON THE DECLINE

New photometric observations were obtained in 1991 to monitor the acti ve galactic nucleus of the Seyfert galaxy NGC 4151 at optical waveleng ths (5672 angstrom continuum and U-band). The results show that the en ergy output from the nucleus of the galaxy has reached peak values par ticularly in the U-band where a rise of 1.3 mag, probably the biggest ever detected in the recorded history of the galaxy, was observed with respect to its mean value of the 1987 quiescent phase. This activity seems however to be on the decline (March 1991). If this is not a spur ious event, an 8 yr time span scale between the 1983 and 1991 maxima m ight be relevant to the power mechanism responsible for the activity o f the nucleus.