X-ray Variability of the Seyfert 1 Markarian 335: Power Spectrum and Time Lags

TL;DR

This study analyzes the X-ray variability and time lags in Seyfert 1 galaxy Markarian 335, revealing power spectrum characteristics and energy-dependent lags consistent with models of propagating fluctuations in accretion flows, similar to black hole X-ray binaries.

Contribution

It provides detailed measurements of the power spectrum and energy-dependent time lags in Markarian 335, supporting the propagating fluctuations model of X-ray variability.

Findings

Power spectrum fits a bending power law with a predicted bend time-scale.

Time lags vary as 1/f at low frequencies and cut off near the bend frequency.

Lag length increases with energy separation in an almost log-linear relation.

Abstract

To investigate further the comparison between AGN and black hole X-ray binaries, we have studied the main X-ray variability properties of the Seyfert 1 Galaxy Markarian 335. We put particular emphasis on the X-ray time lags, which is a potentially important diagnostic of physical models. From a 100 ksec observation by XMM-Newton we show that the power spectrum of this source is well fitted by a bending power law model, and the bend time-scale Tb is precisely at the value predicted by the Tb vs Hbeta line-width relation of McHardy et al. Variations in different energy bands show time-scale dependent time lags, where higher energy bands lag lower ones. The lag, tau, varies as a function of the Fourier frequency, f, of the variability component in the light curves as tau propto 1/f at low frequencies, but there is a sharp cut-off in the lags at a frequency close to the bend frequency in the power spectrum. Similar behaviour is seen in black hole X-ray binary systems. The length of the time lags increases continuously with energy separation, in an almost log-linear relation. We show that the lag spectra can be produced by fluctuations propagating through the accretion flow as long as the energy spectrum of the X-ray emitting region hardens towards the centre.