A global look at X-ray time lags in Seyfert Galaxies

TL;DR

This study analyzes X-ray time lags in 43 Seyfert galaxies, revealing widespread reverberation effects and correlations with black hole properties, enhancing understanding of the inner accretion flow and coronal emission.

Contribution

It expands reverberation studies to a large sample, demonstrating prevalent iron K lags and their relation to black hole mass and accretion rate.

Findings

50% of sources show iron K reverberation.

85% exhibit long-timescale low-frequency hard lags.

Coronal height correlates with mass accretion rate.

Abstract

X-ray reverberation, where light-travel time delays map out the compact geometry around the inner accretion flow in supermassive black holes, has been discovered in several of the brightest, most variable and well-known Seyfert galaxies. In this work, we expand the study of X-ray reverberation to all Seyfert galaxies in the XMM-Newton archive above a nominal rms variability and exposure level (a total of 43 sources). 50 per cent of source exhibit iron K reverberation, in that the broad iron K emission line responds to rapid variability in the continuum. We also find that on long timescales, the hard band emission lags behind the soft band emission in 85 per cent of sources. This `low-frequency hard lag' is likely associated with the coronal emission, and so this result suggests that most sources with X-ray variability show intrinsic variability from the nuclear region. We update the known iron K lag amplitude vs. black hole mass relation, and find evidence that the height or extent of the coronal source (as inferred by the reverberation time delay) increases with mass accretion rate.