Discovery of Narrow and Variable Lines in the Ultraviolet Spectrum of the Seyfert Galaxy NGC 4151, and an Outline of Our Previous Results

Abstract

Extensive observations of NGC 4151 when the nucleus is at a minimum have led to the discovery of two emission lines which have a full width at half maximum of less than 7 and 16 Å respectively (after correction for the instrumental profile) and which vary in intensity by a factor of 3 in less than 10 days. These lines appear on either side of the CIVλ1550 line at λ_rest = 1518.5, 1594.4 Å.

Regardless of their identifications these lines are too narrow to be emitted by the whole broad line region. They must come instead from two localized regions which have a special excitation mechanism.

No identifications for these lines, for example with transitions excited by fluorescence, have been found. An attractive — but speculative — possibility is that the regions emitting them are associated with a two-sided jet reminiscent of SS 433.