Accretion flow diagnostics with X-ray spectral-timing: the hard state of SWIFT J1753.5–0127

Recent XMM-Newton studies of X-ray variability in the hard states of black hole X-ray binaries (BHXRBs) imply that the variability is generated in the ‘standard ’ optically-thick accretion disc that is responsible for the multicolour black-body emission. The variability originates in the disc as mass-accretion fluctuations and propagates through the disc to ‘light up ’ inner disc regions, eventually modulating the power-law emission that is produced relatively centrally. Both the covariance spectra and time lags that cover the soft band strongly support this scenario. Here we present a comparative spectral-timing study of XMM-Newton data from the BHXRB SWIFT J1753.5–0127 in a bright 2009 hard state with that from the significantly fainter 2006 hard state, to show for the first time the change in disc spectral-timing properties associated with a global increase in both the accretion rate and the relative contribution of the disc emission to the bolometric luminosity. We show that, although there is strong evidence for intrinsic disc variability in the more luminous hard state, the disc variability amplitude is suppressed relative to tha