Optical Variability of Narrow‐Line Seyfert 1 Galaxies

We present results of a broad-band photometric study of the opticalvariability of six Narrow-Line Seyfert 1 (NLS1) galaxies observed at 172epochs. We searched for microvariability on 33 nights. Strong evidence formicrovariability was found only for our lowest luminosity object, NGC 4051, onone night. Weaker evidence suggests such variability on a few other nights fortwo other objects, but the data are not as convincing. Intra-night variabilityin NLS1s is thus concluded to be rare and of low amplitude. We giveillustrations of how variable image quality can produce spurious variability.We find that for well-studied non-NLS1s there is a spread in the amplitude ofseasonal variability (i.e., in some years an AGN is more variable than inothers). We find that the means of the variability amplitudes of non-NLS1s overseveral seasons vary from object to object (i.e., some AGNs are, on average,more variable than others). NLS1s also show a spread in seasonal variabilities.The best-studied NLS1, Ark 564, shows a range of amplitudes of variability fromseason to season that is comparable to the range found in BLS1s, and in oneseason Ark 564 was as variable as the most variable non-NLS1. The seasonalamplitudes of variability for NLS1s are mostly in the lower half of the rangeof non-BLS1 seasonal amplitudes, but the absence of a suitable control samplemakes a precise comparison difficult. However, on long timescales (weeks toyears), NLS1s as a class are not more variable than non-NLS1s. The extremevariability seen in the X-rays was not seen in the optical. This hasconsequences for the models of AGNs in general as well as NLS1s in particular.Comment: Astrophysical Journal in press (tentatively scheduled for Vol. 608, June 2004 issue);47 pages; 19 figures. Electronic tables not included (contact first author if needed