The variability characteristics of broad and narrow line Seyfert 1 galaxies.

摘要

The study of variability in Broad and Narrow Line Seyfert 1 galaxies has remained focused primarily on variations in the X-ray flux of these objects. Optical studies to detect variability in Broad Line Seyfert 1 galaxies have indicated variations only on longer timescales. We present the results of an intensive search for variations on timescales of minutes to hours in a sample of Broad and Narrow Line Seyfert 1 galaxies. These results indicate that Narrow Line Seyfert 1 galaxies show very little optical variation, in stark contrast to their behavior in the X-ray regime. Of our sample of 14 NLS 1 galaxies, only 1 showed a positive detection of short timescale variability. Tests of the excess variance of the light curves confirmed the very low level of variations seen in this class of object. Broad Line Seyfert 1 galaxies appear to show higher levels of variability, with duty cycles comparable to that found previously for Radio Quiet QSOs. We report the results of a coordinated multiwavelength campaign on the Broad Line Seyfert 1 galaxy, AKN 120, with concurrent X-ray and optical observations spanning more than two years with sampling every three days, as well as three days of nearly uninterrupted observations. Cross correlations of the two data sets indicate that the variations are simultaneous to within the sampling timescale; i.e. consistent with no lag of one waveband behind the other. Structure function analysis indicated a possible variability timescale of 530 days. The combined PDS of the short and long timescale observations showed a high frequency inflection at 4.4 hours, a slope of −2, and a low frequency inflection at 19 days. The latter inflection indicates a black hole mass of ∼108 solar masses for the central object of AKN 120. A single OSSE observation of AKN 120 was obtained while the object was in a faint state, and is consistent with a high-energy cutoff at 50 to 500 keV.