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X-ray spectral timing analysis is presented of XMM-Newton observations of thenarrow line Seyfert 1 galaxy I Zwicky 1 (I Zw 1) taken in 2015 January. Afterexploring the effect of background flaring on timing analyses, X-ray time lagsbetween the reflection-dominated 0.3-1.0keV energy and continuum-dominated1.0-4.0keV band are measured, indicative of reverberation off the inneraccretion disc. The reverberation lag time is seen to vary as a step functionin frequency; across lower frequency components of the variability, 3e-4 to1.2e-3Hz a lag of 160s is measured, but the lag shortens to (59 +/- 4)s above1.2e-3Hz. The lag-energy spectrum reveals differing profiles between theseranges with a change in the dip showing the earliest arriving photons. The lowfrequency signal indicates reverberation of X-rays emitted from a coronaextended at low height over the disc while at high frequencies, variability isgenerated in a collimated core of the corona through which luminosityfluctuations propagate upwards. Principal component analysis of the variabilitysupports this interpretation, showing uncorrelated variation in the spectralslope of two power law continuum components. The distinct evolution of the twocomponents of the corona is seen as a flare passes inwards from the extended tothe collimated portion. An increase in variability in the extended corona wasfound preceding the initial increase in X-ray flux. Variability from theextended corona was seen to die away as the flare passed into the collimatedcore leading to a second sharper increase in the X-ray count rate.

Revealing structure and evolution within the corona of the Seyfert galaxy I Zw 1