X-ray spectral variability in NGC 3783

TL;DR

This study analyzes Suzaku observations of NGC 3783, revealing intrinsic variability in the X-ray emission and suggesting changes in reflection or ionization near the black hole, with the warm absorber remaining stable.

Contribution

It demonstrates that broad-band X-ray variability is intrinsic to the source and identifies a variable reflection component near the black hole, advancing understanding of AGN spectral variability.

Findings

Warm absorber remains unchanged during variability

Detection of a hard excess at ~20keV indicating additional variable component

Variations likely linked to reflection fraction or ionization state

Abstract

NGC 3783 was observed for approximately 210ks by Suzaku and in this time showed significant spectral and flux variability at both short (20ks) and long (100ks) time scales. The full observation is found to consist of approximately six "spectral periods" where the behaviour of the soft (0.3-1.0keV) and hard (2-10keV) bands are somewhat distinct. Using a variety of methods we find that the strong warm absorber present in this source does not change on these time scales, confirming that the broad-band variability is intrinsic to the central source. The time resolved difference-spectra are well modelled with an absorbed powerlaw below 10keV, but show an additional hard excess at ~20keV in the latter stages of the observation. This suggests that, in addition to the variable powerlaw, there is a further variable component that varies with time but not monotonically with flux. We show that a likely interpretation is that this further component is associated with variations in the reflection fraction or possibly ionization state of the accretion disk a few gravitational radii from the black hole.