Gourgouliatos, KN and Hollerbach, R (2018) Magnetic Axis Drift and Magnetic Spot Formation in Neutron Stars with Toroidal Fields. Astrophysical Journal, 852 (1). 21. ISSN 0004-637X
Abstract
We explore magnetic field configurations that lead to the formation of magnetic spots on the surface of neutron stars and the displacement of the magnetic dipole axis. We find that a toroidally dominated magnetic field is essential for the generation of a single spot with a strong magnetic field. Once a spot forms, it survives for several million years, even after the total magnetic field has decayed significantly. We find that the dipole axis is not stationary with respect to the neutron star's surface and does not in general coincide with the location of the magnetic spot. This is due to non-axisymmetric instabilities of the toroidal field that displace the poloidal dipole axis at rates that may reach 0fdg4 per century. A misaligned poloidal dipole axis with the toroidal field leads to more significant displacement of the dipole axis than the fully aligned case. Finally we discuss the evolution of neutron stars with such magnetic fields on the $P\mbox{--}\dot{P}$ diagram and the observational implications. We find that neutron stars spend a very short time before they cross the Death Line of the $P\mbox{--}\dot{P}$ diagram, compared to their characteristic ages. Moreover, the maximum intensity of their surface magnetic field is substantially higher than the dipole component of the field. We argue that SGR 0418+5729 could be an example of this type of behavior, having a weak dipole field, yet hosting a magnetic spot responsible for its magnetar behavior. The evolution on the pulse profile and braking index of the Crab pulsar, which are attributed to an increase of its obliquity, are compatible with the anticipated drift of the magnetic axis.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2017. The American Astronomical Society. All rights reserved. This is an author produced version of a paper published in Astrophysical Journal. Uploaded in accordance with the publisher's self-archiving policy. |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Engineering & Physical Sciences (Leeds) > School of Mathematics (Leeds) > Applied Mathematics (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 29 Nov 2017 11:36 |
Last Modified: | 25 Jan 2018 08:54 |
Status: | Published |
Publisher: | American Astronomical Society |
Identification Number: | 10.3847/1538-4357/aa9d93 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:124606 |