Timing evidence in determining the accretion state of the Seyfert galaxy NGC 3783

Abstract

Previous observations with the Rossi X-ray Timing Explorer (RXTE) have suggested that the power spectral density (PSD) of NGC 3783 flattens to a slope near zero at low frequencies, in a similar manner to that of Galactic black hole X-ray binary systems (GBHs) in the `hard' state. The low radio flux emitted by this object, however, is inconsistent with a hard state interpretation. The accretion rate of NGC 3783 (~7% of the Eddington rate) is similar to that of other AGN with `soft' state PSDs and higher than that at which the GBH Cyg X-1, with which AGN are often compared, changes between `hard' and `soft' states (~2% of the Eddington rate). If NGC 3783 really does have a `hard' state PSD, it would be quite unusual and would indicate that AGN and GBHs are not quite as similar as we currently believe. Here we present an improved X-ray PSD of NGC 3783, spanning from ~10^{-8} to ~10^{-3} Hz, based on considerably extended (5.5 years) RXTE observations combined with two orbits of continuous observation by XMM-Newton. We show that this PSD is, in fact, well fitted by a `soft' state model which has only one break, at high frequencies. Although a `hard' state model can also fit the data, the improvement in fit by adding a second break at low frequency is not significant. Thus NGC 3783 is not unusual. These results leave Arakelian 564 as the only AGN which shows a second break at low frequencies, although in that case the very high accretion rate implies a `very high', rather than `hard' state PSD. The break frequency found in NGC 3783 is consistent with the expectation based on comparisons with other AGN and GBHs, given its black hole mass and accretion rate.

MNRAS accepted

References in corpus (4)

• Accretion states and radio loudness in Active Galactic Nuclei: analogies with X-ray binaries
• Jet-dominated advective systems: radio and X-ray luminosity dependence on the accretion rate
• Spectral-timing evidence for a Very High State in the Narrow Line Seyfert 1 Ark 564
• Probing the temporal variability of Cygnus X-1 into the soft state

Cited by in corpus (9)

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• Delving into the depths of NGC 3783 with XRISM III. Birth of an ultrafast outflow during a soft flare
• Modelling variability power spectra of active galaxies from irregular time series
• Ultraviolet spectroscopy of the black hole X-ray binary MAXI J1820+070 across a state transition