Night-to-night variation in the optical emission lines in the nuclear spectrum of the Seyfert galaxy NGC 3227
Abstract:Fifty-three spectrograms in the optical region (3700–7300 Å)with a spectral resolution of about 8 Å have been obtained for the Seyfert nucleus of the galaxy NGC 3227 with the 6 m telescope on 12–15 January 1977 while the nucleus was in the historically important epoch of its extreme maximum brightness. The width of the slit was 1?, and the length of the box during the spectral measurements was 1.5?. The data obtained by us and those compiled from literature showed that profiles of the Balmer lines Ha, Hß and H? are different, demonstrating that the gas emitting these lines is highly self-absorbed. The profiles of the Balmer lines contain various components that kept their positions (radial velocities) over 10 years. The components can reflect long-lived flows or jets in the broad-line region (BLR). A blue bump at a radial velocity of -5000 km s -1 in the H? profile was revealed. Variations in the intensities of the revealed components and broad wings of the emission lines Hß and H? profiles were detected over 3 days. The same variations were observed by us earlier in the emission line profiles of the NGC 7469 nucleus spectrum. We suppose that the revealed night-to-night variability of the emission line spectra of the galaxies NGC 3227 and NGC 7469 is a result of short-time flares in the BLR. The dimension of the flare region is less than 0.2 of the whole BLR dimension. The density of the flare region is two to three orders of magnitude higher than that of the overall BLR. One of the possible explanations for the observed event can be proposed in the framework of a model of short-lived shocks in long-lived flows or jets.
Document Type: Research Article
Affiliations: Crimean Astrophysical Observatory, Ukraine and Isaac Newton Institute of Chile, Crimean Branch, 98409, Nauchny, Crimea
Publication date: 2004-12-01