Sandra Denise Clements

The longer optical time scales of a large sample of quasars

Of a carefully studied sample of 60 quasars, 75% displayed evidence of long-term changes in the base levels of their optical fluxes. Internally consistent light curves were analyzed by three different methods in an effort to assign time scales to these changes. The familiar rapid, large-amplitude flares were specifically excluded from the study. The majority of the observed time scales range from 3 to 15 yr, but when they are translated into the rest frames of the objects, there is a strong concentration between 2 and 6 yr.

Correlated radio and optical variations in a sample of AGN

Radio light curves of 20 sources from the Metsahovi monitoring program are compared with optical light curves collected from the literature. The Discrete Correlation Function analysis is applied to the data sets. A new qualitative method to study correlations is introduced, where the radio light curves are replaced by model light curves consisting of exponential outbursts. The optical flux level is compared to the phase and flux level of the model flares. Seven sources show clear correlations using the DCF analysis with six more showing a possible correlation between optical and radio events with time lags from zero to several hundred days. For twelve sources at least one simultaneous optical and radio event is seen. For eleven sources, when comparing optical flux levels with the phase of the model radio outbursts, the optical flux levels were high at the peak of the model radio outbursts. For sixteen sources, when comparing the optical flux level with the radio model flare flux level, the optical flux level was high when radio flux level was high, as well.

THE MULTIFREQUENCY SPECTRAL EVOLUTION OF BLAZAR 3C 345 DURING THE 1991 OUTBURST

The blazar 3C 345 underwent a 2.5 mag optical outburst between 1990 November and 1991 May. We have obtained 10 nearly simultaneous multifrequency spectra during the course of the outburst in order to study the multifrequency spectral variations of 3C 345 as a function of time. Although our observations were not sampled frequently enough to completely resolve the variations in every frequency band, the general rise and decline of the outburst were seen in the UV through radio with differing rise times. Simulations of an electron distribution injected into a tangled magnetic field show a relationship between frequency and characteristic timescale that was also observed in the radio variations of 3C 345. The two X-ray observations made during the monitoring period showed no evidence of variability. The multifrequency spectrum was modeled with two major components: a relativistic jet and a relativistic thermal accretion disk. Models calculated for each spectrum indicate that the outburst can be explained in terms of these models by varying the high-energy cutoff of the injected electron distribution in the jet model, while also varying the mass accretion rate in the disk model. There is marginal evidence that the inferred accretion rate varies with the jet luminosity.

Multiwavelength Evolution of the 1991 Outburst of 3C 345

Data resulting from multiwavelength observations the blazar QSO 3C 345 during a 2.5 magnitude optical outburst of were presented and discussed.