The structure of a Quasi-Keplerian accretion disk around magnetized stars

Habumugisha, Isaac; Jurua, Edward; Tessema, Solomon B; Anguma, Simon Katrini

The structure of a Quasi-Keplerian accretion disk around magnetized stars

Date

2018-06-04

Authors

Habumugisha, Isaac

Jurua, Edward

Tessema, Solomon B

Anguma, Simon Katrini

Publisher

The American Astronomical Society

Abstract

In this paper, we present the complete structure of a quasi-Keplerian thin accretion disk with an internal dynamo around a magnetized neutron star. We assume a full quasi-Keplerian disk with the azimuthal velocity deviating from the Keplerian fashion by a factor of ξ (0 < ξ < 2). In our approach, we vertically integrate the radial component of the momentum equation to obtain the radial pressure gradient equation for a thin quasi-Keplerian accretion disk. Our results show that, at large radial distance, the accretion disk behaves in a Keplerian fashion. However, close to the neutron star, pressure gradient force (PGF) largely modiﬁes the disk structure, resulting into sudden dynamical changes in the accretion disk. The corotation radius is shifted inward (outward) for ξ > 1 (for ξ < 1), and the position of the inner edge with respect to the new corotation radius is also relocated accordingly, as compared to the Keplerian model. The resulting PGF torque couples with viscous torque (when ξ < 1) to provide a spin-down torque and a spin-up torque (when ξ > 1) while in the advective state. Therefore, neglecting the PGF, as has been the case in previous models, is a glaring omission. Our result has the potential to explain the observable dynamic consequences of accretion disks around magnetized neutron stars.

Keywords

Accretion, Accretion disks, Dynamo – stars, Neutron – X-rays

Citation

Habumugisha, I., Jurua, E., Tessema, S. B., & Simon, A. K. (2018). The Structure of a Quasi-Keplerian Accretion Disk around Magnetized Stars. The Astrophysical Journal, 859(2), 147.