Modelling correlated variability in accreting black holes: the effect of high density and variable ionisation on reverberation lags

Abstract

We present a new release of the RELTRANS model to fit the complex cross-spectrum of accreting black holes as a function of energy. The model accounts for continuum lags and reverberation lags self-consistently in order to consider the widest possible range of X-ray variability timescales. We introduce a more self-consistent treatment of the reverberation lags, accounting for how the time variations of the illuminating flux change the ionisation level of the accretion disc. This process varies the shape of the reflection spectrum in time causing an additional source of lags besides the light crossing delay. We also consider electron densities in the accretion disc up to $10^{20}$ cm${}^{-3}$, which are found in most of the stellar mass black holes and in some AGN. These high densities increase the amplitude of the reverberation lags below $1$ keV since the reflection flux enhances in the same energy range. In addition, we investigate the properties of hard lags produced by variations in the power-law index of the continuum spectrum, which can be interpreted as due to roughly $3\%$ variability in the corona's optical depth and temperature. As a test case, we simultaneously fit the lag energy spectra in a wide range of Fourier frequency for the black hole candidate MAXI J1820+070 observed with NICER. The best fit shows how the reverberation lags contribute even at the longer timescales where the hard lags are important. This proves the importance of modelling these two lags together and self-consistently in order to constrain the parameters of the system.

Accepted for publication in MNRAS

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Cited by in corpus (23)

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• The Effect of Returning Radiation on Relativistic Reflection
• Phase-resolved spectroscopy of a quasi-periodic oscillation in the black hole X-ray binary GRS 1915+105 with NICER and NuSTAR
• Dual-Corona Comptonization model for the Type-B Quasi-Periodic Oscillations in GX 339-4
• MAXI J1820+070 X-ray spectral-timing reveals the nature of the accretion flow in black hole binaries
• Investigating the impact of vertically extended coronae on X-ray reverberation mapping
• Long term variability of Cygnus X-1. VIII. A spectral-timing look at low energies with NICER
• X-ray Reverberation Mapping of Ark 564 using Gaussian Process Regression
• A reflection model with a radial disk density profile
• Accretion Scenario of MAXI J1820+070 during 2018 Outbursts with Multi-mission Observations
• A broadband spectral-timing study of QPOs in the bright black hole X-ray binary Swift J1727.8-1613
• Timing analysis of the black-hole candidate Swift J1727.8-1613: detection of a dip-like feature in the high-energy cross spectrum
• On measuring the Hubble constant with X-ray reverberation mapping of active galactic nuclei
• The origin of long soft lags and the nature of the hard-intermediate state in black hole binaries
• Probing black-hole accretion through time variability
• Evidence for a dynamic corona in the short-term time lags of black hole X-ray binary MAXI J1820+070
• Relativistic reflection within an extended hot plasma geometry
• Relativistic Reflection Modeling in AGN and Related Variability from PCA: A Brief Review
• Reverberation lags viewed in hard X-rays from an accreting stellar-mass black hole
• The Reliability of Accretion Disk Inclination Derived from X-ray Spectroscopy of Active Galaxies
• Variable QPO lags and reduced coherence between the disc and corona in MAXI J1820+070
• Measuring black hole spins with x-ray reflection spectroscopy: A GRMHD outlook
• X-ray reflection spectroscopy with improved calculations of the emission angle