Multi-wavelength Variability of the Broad Line Radio Galaxy 3C 120
  We present results from a multi-year monitoring campaign of the broad-line
radio galaxy 3C 120, using the Rossi X-ray Timing Explorer (RXTE) for nearly
five years of observations. Additionally, we present coincident optical
monitoring using data from several ground-based observatories. Both the X-ray
and optical emission are highly variable and appear to be strongly correlated,
with the X-ray emission leading the optical by 28 days. The X-ray power density
spectrum is best fit by a broken power law, with a low-frequency slope of -1.2,
breaking to a high-frequency slope of -2.1, and a break frequency of log
nu_b=-5.75 Hz, or 6.5 days. This value agrees well with the value expected
based on 3C 120's mass and accretion rate. We find no evidence for a second
break in the power spectrum. Combined with a moderately soft X-ray spectrum
(Gamma=1.8) and a moderately high accretion rate (mdot / mdot_Edd ~ 0.3), this
indicates that 3C 120 fits in wellwith the high/soft variability state found in
most other AGNs. Previous studies have shown that the spectrum has a strong Fe
K-alpha line, which may be relativistically broadened. The presence of this
line, combined with a power spectrum similar to that seen in Seyfert galaxies,
suggests that the majority of the X-ray emission in this object arises in or
near the disk, and not in the jet.
