In this research thesis, the variability of active galactic nuclei is
studied using photometric and spectroscopic methods. For this study, two
monitoring campaigns were performed, and their data was analyzed and compared
to existing results. The first campaign was photometric monitoring of 21
quasars from the Sloan Digitized Sky Survey (SDSS) sample. The main purpose of
this campaign was to correlate the physical and variability parameters of these
objects and compare it to existing relations. The objects were monitored over a
period of two years, between 2006 and 2008, at the Wise observatory in Mitzpe-Ramon , Israel. The results of this campaign were added to existing data, taken from
previous works, on objects in the SDSS sample and additional objects in the
Palomar-Green sample. This data also includes physical parameters like
redshift, black hole mass and luminosity. Correlations were made between the
physical parameters and themselves, and between the physical parameters and the
variability parameters. Correlations reported by previous studies have also
been noticed during this campaign. Among them, are the very powerful black hole
mass - luminosity relation and the somewhat weak black hole mass - magnitude
variability gradient. These black hole mass correlations give the relations MBH~LR(1.57)
and log(MBH)~-4<grad R>. A new correlation was noticed, which
was not noted in previous works, between the luminosity and the magnitude
variability gradient. This correlation gives the relation log(LR)~-2.2<grad
R>.
The second campaign was spectroscopic study of two quasars, V396HER and
SDSS135724, both showing variability in their visible waveband emission. The
main purpose of this campaign was to use reverberation mapping in order to
estimate the broad line region and the black hole mass of the objects and
compare it to the black hole mass - luminosity and broad line region -
luminosity relations from previous studies. For both objects, the spectra were
taken with the 9.2 meters Hobby-Eberly Telescope, or HET, which is located at
McDonald observatory. Reverberation mapping was performed on the continuum and
the broad emission lines, resulting in the black hole masses and the broad line
region radius of the objects. All the results are elaborated in the 'Results
and Discussion' section of the work. The main finding in this campaign was that
the black hole mass and broad line region size that were calculated using
reverberation mapping did not agree with the values found by using the two
luminosity relations. Only one value, the black hole mass of V396HER, seemed to
agree between these two methods.
