Revealing a hard X-ray spectral component that reverberates within one light hour of the central supermassive black hole in Ark 564

Abstract

Ark 564 (z=0.0247) is an X-ray-bright NLS1. By using advanced X-ray timing techniques, an excess of "delayed" emission in the hard X-ray band (4-7.5 keV) following about 1000 seconds after "flaring" light in the soft X-ray band (0.4-1 keV) was recently detected. We report on the X-ray spectral analysis of eight XMM-Newton and one Suzaku observation of Ark 564. High-resolution spectroscopy was performed with the RGS in the soft X-ray band, while broad-band spectroscopy was performed with the EPIC-pn and XIS/PIN instruments. We analysed time-averaged, flux-selected, and time-resolved spectra. Despite the strong variability in flux during our observational campaign, the broad-band spectral shape of Ark 564 does not vary dramatically and can be reproduced either by a superposition of a power law and a blackbody emission or by a Comptonized power-law emission model. High-resolution spectroscopy revealed ionised gas along the line of sight at the systemic redshift of the source, with a low column density and a range of ionisation states. Broad-band spectroscopy revealed a very steep intrinsic continuum and a rather weak emission feature in the iron K band; modelling this feature with a reflection component requires highly ionised gas. A reflection-dominated or an absorption-dominated model are similarly able to well reproduce the time-averaged data from a statistical point of view, in both cases requiring contrived geometries and/or unlikely physical parameters. Finally, through time-resolved analysis we spectroscopically identified the "delayed" emission as a spectral hardening above ~4 keV; the most likely interpretation for this component is a reprocessing of the "flaring" light by gas located at 10-100 r_g from the central supermassive black hole that is so hot that it can Compton-upscatter the flaring intrinsic continuum emission.

arXiv comment14 pages, 7 tables, 12 figures. Accepted for publication in A&A. Revised after language editing. Abstract abridged

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Cited by in corpus (12)

• A global view of the inner accretion and ejection flow around super massive black holes: radiation driven accretion disk winds in a physical context
• The high-Eddington NLS1 Ark 564 has the coolest corona
• Relativistic X-ray reverberation modelling of the combined time-averaged and lag-energy spectra in AGN
• Testing the Kerr nature of the supermassive black hole in Ark 564
• Direct probe of the inner accretion flow around the supermassive black hole in NGC 2617
• NuSTAR observation of Ark 564 reveals the variation of coronal temperature with flux
• X-ray Reverberation Mapping of Ark 564 using Gaussian Process Regression
• On the Nature of the High-Energy Rollover in 1H 0419-577
• The warm absorber in the radio-loud quasar 4C +74.26
• Probing the photoionised outflow in the NLS1 Ark 564: An XMM-Newton view
• Effects of ultra-fast outflows on X-ray time lags in AGN
• UV and X-Ray Variability of the Narrow-Line Seyfert 1 Galaxy Ark 564