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Angular Momentum Transfer in the Binary X-ray Pulsar GX 1+4*

Published online by Cambridge University Press:  05 March 2013

J. G. Greenhill ,
D. K. Galloway  and
J. R. Murray
J. G. Greenhill
Affiliation:
School of Mathematics and Physics, University of Tasmania, GPO Box 252–21, Hobart, Tas. 7005, Australia; [email protected]
D. K. Galloway
Affiliation:
School of Mathematics and Physics, University of Tasmania, GPO Box 252–21, Hobart, Tas. 7005, Australia Research Centre for Theoretical Astrophysics, University of Sydney, Sydney, NSW 2006, Australia; [email protected]
J. R. Murray
Affiliation:
Department of Physics and Astronomy, University of Leicester, University Rd, Leicester, LE1 7RH, UK; [email protected]
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Abstract

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Optical and X-ray spectroscopy indicate that the X-ray pulsar GX 1+4 is seen through a cloud of gravitationally bound matter. We discuss an unstable negative feedback mechanism (originally proposed by Kotani et al. 1999), based on X-ray heating of this matter which controls the accretion rate when the source is in a low X-ray luminosity state. A deep minimum lasting ∼6 hours occurred during observations with the RXTE satellite over 1996 July 19–21. The shape of the X-ray pulses changed remarkably from before to after the minimum. These changes may be related to the transition from neutron star spin-down to spin-up which occurred at about the same time. Smoothed particle hydrodynamic simulations of the effect of adding matter with opposite angular momentum to an existing disk, show that it is possible for a number of concentric rings with alternating senses of rotation to co-exist in a disk. This could provide an explanation for the step-like changes in Ṗ which are observed in GX 1+4. Changes at the inner boundary of the disk occur at the same timescale as that imposed at the outer boundary. Reversals of material torque on the neutron star occur at a minimum in LX.

Keywords

accretion, accretion diskspulsars: individual (GX 1+4)stars: winds, outflowsX-rays: starsradiation mechanisms: thermalhydrodynamics
Type
Research Article
Information
Publications of the Astronomical Society of Australia , Volume 16 , Issue 3 , 1999 , pp. 240 - 246
Copyright
Copyright © Astronomical Society of Australia 1999

Footnotes

*

Refereed paper based on three separate contributions to the Workshop on Magnetic Fields and Accretion, held at the Astrophysical Theory Centre, Australian National University, on 12–13 November 1998.

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