A QPO in NGC 4945 from Archival RXTE Data
  We report the discovery of a ~6-week quasi-periodic oscillation (QPO) in
archival NGC 4945 data observed by the Rossi X-ray Timing Explorer (RXTE)
satellite. QPOs are an important observable in accretion disks and have been
studied extensively in both neutron star (NS) and black hole (BH) X-ray
binaries (XRB). QPOs should be present in Active Galactic Nuclei (AGN) if
galactic black holes and supermassive black holes (SMBH) are governed by a
common set of physical processes. The search for QPOs in AGN has proven
difficult because the timescales would be much longer, due to their higher
mass. RXTE AGN light curves spanning 1996 to 2011 provide an excellent and
perhaps unique opportunity to search for low-frequency QPOs. We investigated
the 533 RXTE observations made of the Seyfert-2 AGN, NGC 4945. During a large
cluster of observations in 2006-2007 (194 observations, spanning 396 days), the
Lomb-Scargle periodogram shows a candidate QPO at 0.274 $\mu$Hz (period
$\approx$ 42.2 days). We estimate the uncertainties using the False Alarm
Probability (FAP). We discuss the possible identification of this feature with
the Lense-Thirring precession period.
