X-ray reflection from cold matter in the nuclei of active galaxies

Abstract

THE evidence accumulated over the past few years for strong soft X-ray emission from active galactic nuclei1–3 has been interpreted as black body emission from the innermost stable region of an accretion disk feeding the putative black hole at the centre of the active nucleus, a view given strong support by the rapid variability of some soft X-ray components4. More recently, new X-ray data from the Exosat and Ginga satellites have revealed a second indicator of optically thick matter in the vicinity of the active nucleus, in the form of an iron K-fluorescence line at ≈6.4 keV (refs 5–8). We report the discovery of two further common features of continuum absorption and reflection, revealed in a composite spectrum from twelve Ginga observations of Seyfert-type active galactic nuclei. Most of these spectral features are shown to be well modelled by reprocessing of the hard X-ray power-law continuum in a slab (or perhaps a disk) of cold matter. There is also evidence for a substantial line-of-sight column of photoionized material.

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Pounds, K., Nandra, K., Stewart, G. et al. X-ray reflection from cold matter in the nuclei of active galaxies. Nature 344, 132–133 (1990). https://doi.org/10.1038/344132a0

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