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

ABSTRACT The nature and geometry of the accretion flow in low/hard state black hole binaries is currently controversial. While most properties are generally explained truncated disc/hot inner model, detection a broad residual around iron line argues for strong relativistic effects from an untruncated disc. Since spectral fitting alone somewhat degenerate, we combine it with additional information fast X-ray variability perform full spectral-timing analysis NICER NuSTAR data on bright MAXI J1820+070. We model propagating mass rate fluctuations by combining two separate current insights: that hot spectrally inhomogeneous, there discontinuous jump viscous time-scale between variable Our naturally gives double-humped shape power spectra, increasing high-frequency energy second hump. Including reflection reprocessing disc at few tens gravitational radii quantitatively reproduces switch lag-frequency hard lagging soft low frequencies (propagation through flow) to high (reverberation continuum illuminating disc). derived show how this can be used observationally test ideas about origin jet.