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

TL;DR

This study uses X-ray spectral timing analysis of I Zwicky 1 to reveal how different regions of its corona contribute to X-ray reverberation signals, showing evolving structures and propagation of luminosity fluctuations.

Contribution

It provides new insights into the structure and evolution of the corona in a Seyfert galaxy through detailed timing and spectral analysis, highlighting distinct behaviors at different frequencies.

Findings

Reverberation lag varies with frequency, indicating different coronal regions.

Low-frequency signals suggest an extended corona at low height.

High-frequency signals imply a collimated core with propagating fluctuations.

Abstract

X-ray spectral timing analysis is presented of XMM-Newton observations of the narrow line Seyfert 1 galaxy I Zwicky 1 (I Zw 1) taken in 2015 January. After exploring the effect of background flaring on timing analyses, X-ray time lags between the reflection-dominated 0.3-1.0keV energy and continuum-dominated 1.0-4.0keV band are measured, indicative of reverberation off the inner accretion disc. The reverberation lag time is seen to vary as a step function in frequency; across lower frequency components of the variability, 3e-4 to 1.2e-3Hz a lag of 160s is measured, but the lag shortens to (59 +/- 4)s above 1.2e-3Hz. The lag-energy spectrum reveals differing profiles between these ranges with a change in the dip showing the earliest arriving photons. The low frequency signal indicates reverberation of X-rays emitted from a corona extended at low height over the disc while at high frequencies, variability is generated in a collimated core of the corona through which luminosity fluctuations propagate upwards. Principal component analysis of the variability supports this interpretation, showing uncorrelated variation in the spectral slope of two power law continuum components. The distinct evolution of the two components of the corona is seen as a flare passes inwards from the extended to the collimated portion. An increase in variability in the extended corona was found preceding the initial increase in X-ray flux. Variability from the extended corona was seen to die away as the flare passed into the collimated core leading to a second sharper increase in the X-ray count rate.