Interactions of type I X-ray bursts with thin accretion disks

Abstract

Careful observations of X-ray spectra during type I X-ray bursts have hinted at changes occurring in the inner regions of the accretion disks around the neutron-star component of the binary system. Here, we perform a set of numerical experiments studying the interaction of such bursts with thin, Shakura–Sunyaev-type accretion disks. We now clearly demonstrate a number of key effects that take place simultaneously, including evidence for weak, radiation-driven outflows along the surface of the disk; substantial levels of Poynting–Robertson (PR) drag, leading to enhanced accretion; and prominent heating in the disk, which increases the height, while lowering the density and optical depth. The PR drag causes the inner edge of the disk to retreat from the neutron-star surface toward larger radii and then recover on the timescale of the burst. We conclude that the rich interaction of an X-ray burst with the surrounding disk provides a novel way to study the physics of accretion onto compact objects.

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Fig. 1: Spacetime diagrams of the surface density.
Fig. 2: Track of the inner radius of the accretion disk.
Fig. 3: Spacetime diagrams of the effective optical depth.
Fig. 4: Spacetime diagrams of the mass flux through each radial shell.
Fig. 5: Pseudocolour plot of the mass flux in the meridional plane with streamlines of the velocity field.
Fig. 6: Demonstration of PR drag.

Data availability

The data required to reproduce all figures, except Fig. 5 and Supplementary Fig. 4, are provided in the Source Data. The raw simulation data are available from the corresponding author on reasonable request.

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Acknowledgements

P.C.F. and A.B. acknowledge support from SC NASA EPSCoR RGP 2017 and National Science Foundation grants AST-1616185 and AST-1907850. P.C.F. acknowledges support from National Science Foundation grant PHY-1748958. A.B. acknowledges support from the College of Charleston Undergraduate Research and Creative Activities Board, through SURF grant SU2019-01. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1548562.

Author information

P.C.F. wrote the manuscript with input from all authors. P.C.F. and D.R.B. wrote the funding proposal that supported this work. P.C.F. and A.B. designed and executed the simulations and analysed the results.

Correspondence to P. Chris Fragile.

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Supplementary Information

Supplementary Figs. 1–4.

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Fragile, P.C., Ballantyne, D.R. & Blankenship, A. Interactions of type I X-ray bursts with thin accretion disks. Nat Astron (2020). https://doi.org/10.1038/s41550-019-0987-5

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