Signals from strong field gravity: getting to the physics
06 / 2011 - 08 / 2016
This proposal aims to use the millisecond X-ray time variability signals that are emitted by the plasma flows in the strong field gravity regions of weakly magnetized accreting neutron stars and stellar mass black holes in novel ways, to see the effects of strong gravity and to empirically constrain the properties of the central objects. A number of concrete physical ideas concerning the variability formation mechanisms and their link to X-ray spectral formation is put forward: variability propagation, radiation feedback, and in pulsars the coherent connections expected between flow and surface phenomena. These ideas are used to suggest signal analysis approaches tailored to exhibit signatures of the underlying formation physics: in particular cross- and bi-spectral methods seem appropriate, and initial work in these areas confirms this. Some of these methods have been pioneered by us, and our experience with casting such methods into practical form allowing the routine analysis of large amounts of data by a varied group of researchers will be essential in the proposed work. Computational work on these flows is getting sufficiently concrete as to suggest precise time series characteristics. Dr. Romanova, who with her group at Cornell has recently been producing an exciting series of first results of sophisticated large-scale MHD simulations, has agreed to be part of the team tackling this line of research. Where appropriate we will apply the same methods to data and simulations to help interpretation of both. Work on neutron stars and black holes will proceed in parallel and by cross-comparison will allow powerful tests of all interpretation.