Аннотация
Abstract Spectra of Mrk 474 have been obtained in order to search for short-term (less than one day) variability in the broad Hβ and Hα profiles. Observations were carried out using a slit spectrograph and a three-cascade image tube attached to the 70-cm reflector. The processing of the series of spectrograms, obtained on 1999 April 25, showed a rapid (less than 20 minutes) and powerful increase of the flux in the region of [O III]λ5007. The increase of the flux near maximum (5060Å ± 10Å)appeared to be equal approximately to 300%. The value similar to the FWHM for the long-wavelength excess of the flux was equal to 170Å ± 20Å. The dying-out of the long-wavelength excess lasted approximately two hours.