The long term X-ray time-lags of NGC 4051

Abstract

We present the long term, frequency-dependent, X-ray time lags of the Seyfert galaxy NGC 4051. We used Rossi X-ray Timing Explorer light curves in the 2-4, 4-7 and 7-10 keV bands and we measured the time-lags at $10^{-7}-10^{-6}$ Hz. This is the lowest frequency range that AGN time-lags have ever been measured. The variations in the higher energy bands are delayed with respect to the variations we observe at 2-4 keV, in agreement with the time-lags at high frequencies. When we combine our results with those from the model fitting of the time lags at higher frequencies we find that that the X-ray hard lags in NGC 4051 follow a power law of slope $\sim -1$ over a broad frequency range, from $\sim 10^{-7}$ to $\sim 10^{-3}$ Hz. This is consistent with the time-lags of Cyg X-1, a result which further supports the analogy between active galaxies and Galactic X-ray black hole binaries.

arXiv commentAccepted for publication in MNRAS

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• A theoretical study of the time-lags due to Comptonization and the constraints on the X-ray corona in AGN
• X-ray Flux and Spectral Variability of the Blazar OJ 287 with Suzaku
• Probing black-hole accretion through time variability
• XMM-Newton detection of soft time lags in the TDE candidate AT 2018fyk