The Closest Look at 1H0707-495: X-ray Reverberation Lags with 1.3 Ms of Data

TL;DR

This study provides an in-depth analysis of X-ray reverberation lags in the AGN 1H0707-495 using 1.3 Ms of data, confirming previous lag features and revealing new insights into the origin of these lags.

Contribution

It offers the most detailed reverberation lag analysis of 1H0707-495 to date, clarifying the physical mechanisms behind observed lag features with advanced simulations.

Findings

Confirmation of a ~100s hard lag at low frequencies

Detection of a ~30s soft lag at higher frequencies

Evidence of Fe K line signature in high-frequency lag spectrum

Abstract

Reverberation lags in AGN were first discovered in the NLS1 galaxy, 1H0707-495. We present a follow-up analysis using 1.3 Ms of data, which allows for the closest ever look at the reverberation signature of this remarkable source. We confirm previous findings of a hard lag of ~100 seconds at frequencies v ~ [0.5 - 4] e-4 Hz, and a soft lag of ~30 seconds at higher frequencies, v ~ [0.6 - 3] e-3 Hz. These two frequency domains clearly show different energy dependences in their lag spectra. We also find evidence for a signature from the broad Fe K line in the high frequency lag spectrum. We use Monte Carlo simulations to show how the lag and coherence measurements respond to the addition of Poisson noise and to dilution by other components. With our better understanding of these effects on the lag, we show that the lag-energy spectra can be modelled with a scenario in which low frequency hard lags are produced by a compact corona responding to accretion rate fluctuations propagating through an optically thick accretion disc, and the high frequency soft lags are produced by short light-travel delay associated with reflection of coronal power-law photons off the disc.