A QPO in NGC 4945 from Archival RXTE Data
Abstract
Quasi-periodic oscillations (QPOs) are an important observable in accretion disk. QPOs have been studied extensively in both neutron star and black hole x-ray binaries (BHXRB), and 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. Some candidate QPOs remain unconfirmed, but two reasonably strong cases have been found, a 0.27-mHz QPO (period = 3733 ± 140 s) in REJ 1034+396, which has been compared with the 67-Hz QPO in the BHXRB GRS1915+105, and a 0.15-mHz QPO (∼2-hr) in MS 2254.9-3712.To look for low-frequency QPOs, we have investigated archival data from the Rossi X-ray Timing Explorer (RXTE) satellite collected between 1996 and 2011. AGN monitoring on a regular cadence was performed for many sources, and reduced light curves have been prepared and archived (Rivers et al., 2013). A total of 533 RXTE observations were 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 27.4 μHz (period = 42.3 days). A folded light curve on this period shows a relatively smooth variation. We also investigate SWIFT BAT data for this source covering the same time period.
- Publication:
-
AAS/High Energy Astrophysics Division
- Pub Date:
- March 2019
- Bibcode:
- 2019HEAD...1710631S