Narrow and variable lines in the ultraviolet spectrum of the Seyfert galaxy NGC4151

The Seyfert galaxy NGC4151 observed when the nucleus is at a minimum has two emission lines of full width at half maximum less than 7 and 16 A, respectively, and varying in intensity by a factor of three in 10 days. These lines are too narrow to be emitted by the whole broad-line region and must arise instead from two localized regions which have a special excitation mechanism, possibly a two-sided jet