Discovery of high-frequency iron K lags in Ark 564 and Mrk 335

TL;DR

This study identifies high-frequency Fe K reverberation lags in Ark 564 and Mrk 335, supporting a relativistic reflection model and revealing distinct physical processes for low and high-frequency lags.

Contribution

First detection of high-frequency Fe K lags in Ark 564 and Mrk 335, expanding the sample of sources with reverberation measurements and supporting the relativistic reflection interpretation.

Findings

High-frequency Fe K lags detected in Ark 564 and Mrk 335.

Lag amplitude scales with black hole mass.

Low-frequency lags show no reverberation features.

Abstract

We use archival XMM-Newton observations of Ark 564 and Mrk 335 to calculate the frequency dependent time-lags for these two well-studied sources. We discover high-frequency Fe K lags in both sources, indicating that the red wing of the line precedes the rest frame energy by roughly 100 s and 150 s for Ark 564 and Mrk 335, respectively. Including these two new sources, Fe K reverberation lags have been observed in seven Seyfert galaxies. We examine the low-frequency lag-energy spectrum, which is smooth, and shows no feature of reverberation, as would be expected if the low-frequency lags were produced by distant reflection off circumnuclear material. The clear differences in the low and high frequency lag-energy spectra indicate that the lags are produced by two distinct physical processes. Finally, we find that the amplitude of the Fe K lag scales with black hole mass for these seven sources, consistent with a relativistic reflection model where the lag is the light travel delay associated with reflection of continuum photons off the inner disc.