I. George

Ark 564 (z=0.0247) is an X-ray bright NLS1. By using advanced X-ray timing techniques, Legg et al. (2012) discovered 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). 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 large variability in flux, the broad band spectral shape of Ark 564 is not dramatically varying 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 the presence of 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 the presence of highly ionised gas. Either a reflection-dominated or an absorption-dominated model are 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 discovered by Legg et al. (2012) as a spectral hardening above ~4 keV; the most likely interpretation for this component is reprocessing of the "flaring" light by gas located at 10-100 r_g from the central supermassive black hole and so hot to be able to Compton upscatter the flaring intrinsic continuum emission.