The evolution of the emission-line spectrum of an active nucleus during a separate active event is considered. It is assumed that: (1) the distribution of line-emitting clouds in the broad-line region is isotropic in relation to the ionizing source; (2) the typical cloud emits in lines mainly from the side illuminated by the source; (3) the luminosity of the typical cloud in a line is proportional to the power s of the incident ionizing flux. The relations are compared to the available data on the spectral variability of the Seyfert galaxy NGC 4151. In particular, it is concluded that the duration and the amplitude of a typical flare of NGC 4151 in the unobservable ionizing continuum both substantially exceed that in the observable X-ray.
- Pub Date:
- July 1988