The X-ray Power Spectral Density Function of the Seyfert Active Galactic Nucleus NGC 7469

TL;DR

This study measures the X-ray power spectral density of NGC 7469, revealing a break frequency consistent with empirical black hole scaling relations and an energy-dependent PSD shape similar to Galactic black hole systems.

Contribution

First broadband X-ray PSD measurement of NGC 7469 showing a significant break and energy-dependent PSD shape, using Monte Carlo methods for reliable parameter estimation.

Findings

Detected a PSD break at ~6-12 days.

Found the 10-20 keV PSD is flatter at high frequencies.

Observed energy-dependent PSD evolution similar to Galactic black holes.

Abstract

We present the broadband X-ray power spectral density function (PSD) of the X-ray-luminous Seyfert 1.2 NGC 7469, measured from Rossi X-ray Timing Explorer monitoring data and two XMM-Newton observations. We find significant evidence for a turnover in the 2-10 keV PSD at a temporal frequency of 2.0(+3.0,-0.8)e-6 Hz or 1.0(+3.0,-0.6)e-6 Hz, depending on the exact form of the break (sharply-broken or slowly-bending power-law, respectively). The ``surrogate'' Monte Carlo method of Press et al. (1992) was used to map out the probability distributions of PSD model parameters and obtain reliable uncertainties (68 per cent confidence limits quoted here). The corresponding break time scale of 5.8 (+/- 3.5) days or 11.6(+17.5,-8.7) days, respectively, is consistent with the empirical relation between PSD break time scale, black hole mass and bolometric luminosity of McHardy et al. Compared to the 2-10 keV PSD, the 10-20 keV PSD has a much flatter shape at high temporal frequencies, and no PSD break is significantly detected, suggesting an energy-dependent evolution not unlike that exhibited by several Galactic black hole systems.