Multi-timescale reverberation mapping of Mrk 335

TL;DR

This study models X-ray reverberation and hard lags in Seyfert galaxy Mrk 335 to estimate black hole mass, revealing discrepancies with optical measurements and highlighting modeling limitations.

Contribution

It introduces a combined spectral and lag modeling approach that accounts for propagating fluctuations and reverberation effects to estimate black hole mass.

Findings

Estimated black hole mass is ~1.1 million solar masses.

Model fits the energy and lag spectra but underestimates the mass compared to optical methods.

Adding variability amplitudes complicates the model's ability to fit reverberation features.

Abstract

Time lags due to X-ray reverberation have been detected in several Seyfert galaxies. The different travel time between reflected and directly observed rays naturally causes this type of lag, which depends directly on the light-crossing timescale of the system and hence scales with the mass of the central black hole. Featureless `hard lags' not associated with reverberation, and often interpreted as propagating mass accretion rate fluctuations, dominate the longer timescale variability. Here we fit our reltrans model simultaneously to the time-averaged energy spectrum and the lag-energy spectra of the Seyfert galaxy Mrk 335 over two timescales (Fourier frequency ranges). We model the hard lags as fluctuations in the slope and strength of the illuminating spectrum, and self-consistently account for the effects that these fluctuations have on the reverberation lags. The resulting mass estimate is $1.1^{+2.0}_{-0.7} \times 10^6~M_\odot$, which is significantly lower than the mass measured with the optical reverberation mapping technique (14 - 26 million $M_\odot$). When we add the correlated variability amplitudes to the time lags by fitting the full complex cross-spectra, the model is unable to describe the characteristic reverberation Fe K$\alpha$ line and cannot constrain the black hole mass. This may be due to the assumption that the direct radiation is emitted by a point-like source.