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

Understand

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.