Looking for the underlying cause of black hole X-ray variability in GRMHD simulations

Bollimpalli, D. A.; Mahmoud, Ra'ad; Done, Chris; Fragile, P. Chris; Kluźniak, W.; Narayan, Ramesh; White, Christopher J.

doi:10.1093/mnras/staa1808

Cited by 20 publications

(14 citation statements)

References 72 publications

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“…9) which match well to our derived viscous time-scales. Other SANE models (Bollimpalli et al 2020) also show similar viscous time-scales to those derived from Narayan et al 2012 and thus match our spectraltiming model.…”

Section: Discussionsupporting

confidence: 83%

A full spectral-timing model to map the accretion flow in black hole binaries: the low/hard state of MAXI J1820+070

Kawamura,

Axelsson,

Done

et al. 2021

Preprint

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The nature and geometry of the accretion flow in the low/hard state of black hole binaries is currently controversial. While most properties are generally explained in the truncated disc/hot inner flow model, the detection of a broad residual around the iron line argues for strong relativistic effects from an untruncated disc. Since spectral fitting alone is somewhat degenerate, we combine it with the additional information in the fast X-ray variability and perform a full spectral-timing analysis for NICER and NuSTAR data on a bright low/hard state of MAXI J1820+070. For the first time, we model the variability with propagating mass accretion rate fluctuations by combining two separate current insights: that the hot flow is spectrally inhomogeneous, and that there is a discontinuous jump in viscous time-scale between the hot flow and variable disc. Our model naturally gives the 'double hump' shape of the power spectra, and the increasing high frequency variability with energy in the second hump. Including reflection quantitatively reproduces the switch in the lag-frequency spectra, from hard lagging soft at low frequencies (propagation through the variable flow) to the soft lagging hard at the high frequencies (reverberation from the hard X-ray continuum illuminating the disc). The light travel time derived from the model corresponds to a distance of ∼ 45 gravitational radii, supporting the truncated disc model geometry for the low/hard state. The propagation lags allow us to measure the viscous time-scale in the hot flow, and the results favour SANE rather than MAD models for this source.

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Section: Discussionsupporting

confidence: 83%

A full spectral-timing model to map the accretion flow in black hole binaries: the low/hard state of MAXI J1820+070

Kawamura,

Axelsson,

Done

et al. 2021

Preprint

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“…Nowak & Vaughan 1996) or downward propagation of mass accretion rate perturbations (e.g. Lyubarskii 1997; Kotov et al 2001;Bollimpalli et al 2020). However, both processes would produce hard X-ray lags, whereas in our case the lag-frequency spectrum is dominated by soft X-ray lags at high frequencies (Fig.…”

Section: Appendix B: Observed Soft X-ray Lag Amplitude and Its Evolution As A Function Of Spectral Hardnessmentioning

confidence: 48%

The inner flow geometry in MAXI J1820+070 during hard and hard-intermediate states

Marco

Zdziarski

Ponti

et al. 2021

A&A

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Context. We present a systematic X-ray spectral-timing study of the recently discovered, exceptionally bright black hole X-ray binary system MAXI J1820+070. Our analysis focuses on the first part of the 2018 outburst, covering the rise throughout the hard state, the bright hard and hard-intermediate states, and the transition to the soft-intermediate state. Aims. We address the issue of constraining the geometry of the innermost accretion flow and its evolution throughout an outburst. Methods. We employed two independent X-ray spectral-timing methods applied to archival NICER data of MAXI J1820+070. We first identified and tracked the evolution of a characteristic frequency of soft X-ray thermal reverberation lags (lags of the thermally reprocessed disc emission after the irradiation of variable hard X-ray photons). This frequency is sensitive to intrinsic changes in the relative distance between the X-ray source and the disc. Then, we studied the spectral evolution of the quasi-thermal component responsible for the observed thermal reverberation lags. We did so by analysing high-frequency covariance spectra, which single out spectral components that vary in a linearly correlated way on the shortest sampled timescales and are thus produced in the innermost regions of the accretion flow. Results. The frequency of thermal reverberation lags steadily increases throughout most of the outburst, implying that the relative distance between the X-ray source and the disc decreases as the source softens. However, near transition this evolution breaks, showing a sudden increase (decrease) in lag amplitude (frequency). On the other hand, the temperature of the quasi-thermal component in covariance spectra, due to disc irradiation and responsible for the observed soft reverberation lags, consistently increases throughout all the analysed observations. Conclusions. This study proposes an alternative interpretation to the recently proposed contracting corona scenario. Assuming a constant height for the X-ray source, the steady increase in the reverberation lag frequency and in the irradiated disc temperature in high-frequency covariance spectra can be explained in terms of a decrease in the disc inner radius as the source softens. The behaviour of thermal reverberation lags near transition might be related to the relativistic plasma ejections detected at radio wavelengths, suggesting a causal connection between the two phenomena. Throughout most of the hard and hard-intermediate state, the disc is consistent with being truncated (with an inner radius Rin ≳ 10 Rg), reaching close to the innermost stable circular orbit only near transition.

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“…Furthermore, it is currently not clear what observational data could be used to constrain the adiabatic index of the flow. For example, Bollimpalli et al (2020) studied the variability of the mass accretion rate in very long numerical simulations of accretion disks with relativistic and non-relativistic adiabatic index. They did not find major qualitative differences between their simulations and their post-processed results, specifically for the variability in the mass accretion rate.…”

Section: Adiabatic Index: R2 Vs R3 and R4 Vs R9mentioning

confidence: 99%

cuHARM : a new GPU accelerated GR-MHD code and its application to ADAF disks

Bégué,

Pe'er,

Zhang

et al. 2022

Preprint

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We introduce a new GPU-accelerated general-relativistic magneto-hydrodynamic (GR-MHD) code based on HARM which we call cuHARM. The code is written in CUDA-C and uses OpenMP to parallelize multi-GPU setups. Our code allows us to run high resolution simulations of accretion disks and the formation and structure of jets without the need of multi-node supercomputer infrastructure. A 256 3 simulation is well within the reach of an Nvidia DGX-V100 server, with the computation being a factor about 10 times faster if only the CPU was used. We use this code to examine several disk structures all in the SANE state. We find that: (i) increasing the magnetic field, while in the SANE state does not affect the mass accretion rate; (ii) Simultaneous increase of the disk size and the magnetic field, while keeping the ratio of energies fixed, lead to the destruction of the jet once the magnetic flux through the horizon decrease below a certain limit. This demonstrates that the existence of the jet is not a linear function of the initial magnetic field strength; (iii) the structure of the jet is a weak function of the adiabatic index of the gas, with relativistic gas tend to have a wider jet.

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Looking for the underlying cause of black hole X-ray variability in GRMHD simulations

Cited by 20 publications

References 72 publications

A full spectral-timing model to map the accretion flow in black hole binaries: the low/hard state of MAXI J1820+070

A full spectral-timing model to map the accretion flow in black hole binaries: the low/hard state of MAXI J1820+070

The inner flow geometry in MAXI J1820+070 during hard and hard-intermediate states

cuHARM : a new GPU accelerated GR-MHD code and its application to ADAF disks

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