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In the past five years, a flurry of X-ray reverberation lag measurements ofaccreting supermassive black holes have been made using the XMM-Newtontelescope in the 0.3-10 keV energy range. In this work, we use the NuSTARtelescope to extend the lag analysis up to higher energies for two Seyfertgalaxies, SWIFT J2127.4+5654 and NGC 1365. X-ray reverberation lags are due tothe light travel time delays between the direct continuum emission and thereprocessed emission from the inner radii of an ionised accretion disc.XMM-Newton has been particularly adept at measuring the lag associated with thebroad Fe K emission line, where the gravitationally redshifted wing of the lineis observed to respond before the line centroid at 6.4 keV, produced at largerradii. Now we use NuSTAR to probe the lag at higher energies, where thespectrum shows clear evidence for Compton reflection, known as the Compton'hump'. The XMM-Newton data show Fe K lags in both SWIFT J2127.4+5654 and NGC1365. The NuSTAR data provide independent confirmation of these Fe K lags, andalso show evidence for the corresponding Compton hump lags, especially in SWIFTJ2127.4+5654. These broadband lag measurements confirm that the Compton humpand Fe K lag are produced at small radii. At low-frequencies in NGC 1365, wherethe spectrum shows evidence for eclipsing clouds in the line of sight, we finda clear negative (not positive) lag from 2--10 keV, which can be understood asthe decrease in column density from a neutral eclipsing cloud moving out of ourline of sight during the observation.

Iron K and Compton hump reverberation in SWIFT J2127.4+5654 and NGC 1365 revealed by NuSTAR and XMM-Newton