The causal connection between disc and power-law variability in hard state black hole X-ray binaries
Abstract
We use the XMM-Newton EPIC-pn instrument in timing mode to extend spectral time-lag studies of hard state black hole X-ray binaries into the soft X-ray band. We show that variations of the disc blackbody emission substantially lead variations in the power-law emission, by tenths of a second on variability time-scales of seconds or longer. The large lags cannot be explained by Compton scattering but are consistent with time-delays due to viscous propagation of mass accretion fluctuations in the disc. However, on time-scales less than a second the disc lags the power-law variations by a few ms, consistent with the disc variations being dominated by X-ray heating by the power-law, with the short lag corresponding to the light-travel time between the power-law emitting region and the disc. Our results indicate that instabilities in the accretion disc are responsible for continuum variability on time-scales of seconds or longer and probably also on shorter time-scales.
Keywords
Cite
@article{arxiv.1104.0634,
title = {The causal connection between disc and power-law variability in hard state black hole X-ray binaries},
author = {P. Uttley and T. Wilkinson and P. Cassatella and J. Wilms and K. Pottschmidt and M. Hanke and M. Boeck},
journal= {arXiv preprint arXiv:1104.0634},
year = {2015}
}
Comments
Accepted for publication in MNRAS Letters