Relativistic iron K X-ray Reverberation in NGC 4151

TL;DR

This paper reports the first detection of relativistic iron K X-ray reverberation in an active galactic nucleus, NGC 4151, revealing inner accretion disk reflection effects through timing analysis.

Contribution

It presents the first timing-based detection of a broad iron K line in an AGN, demonstrating reverberation delays consistent with relativistic reflection.

Findings

Detection of ~2000 s reverberation delays in NGC 4151

Lag profile resembles a relativistically broadened iron line

Lag peak shifts to lower energies at higher frequencies

Abstract

Recent X-ray observations have enabled the study of reverberation delays in AGN for the first time. All the detections so far are in sources with a strong soft excess, and the measured delay is between the hard (1-3 keV) direct continuum and the soft excess (0.5-1 keV), interpreted as the reflection continuum smeared by relativistic effects. There is however an inherent ambiguity in identifying and studying the details of the lines in the soft excess. Here we report the first detection of reverberation in the iron K band in any AGN. Using XMM-Newton observations of NGC 4151, we find delays of order 2000 s on time-scales of 10e5 s between the 5-6 keV band and 2-3 and 7-8 keV bands, with a broad lag profile resembling a relativistically-broadened iron line. The peak of the lag spectra shifts to lower energies at higher frequencies, consistent with the red wing of the line being emitted at smaller radii, as expected from reflection off the inner accretion disk. This is a first detection of a broad iron line using timing studies.