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Pulsar Timing irregularities and the imprint of magnetic field evolution

Pons, Jose and Viganno, Daniele and Geppert, Ulrich (2012) Pulsar Timing irregularities and the imprint of magnetic field evolution. Astronomy and Astrophysics, 547 (A9). EDP Sciences. DOI: 10.1051/0004-6361/201220091

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Abstract

Context. The rotational evolution of isolated neutron stars is dominated by the magnetic field anchored to the solid crust of the star. Assuming that the core field evolves on much longer timescales, the crustal field evolves mainly though Ohmic dissipation and the Hall drift, and it may be subject to relatively rapid changes with remarkable effects on the observed timing properties. Aims. We investigate whether changes of the magnetic field structure and strength during the star evolution may have observable consequences in the braking index n. This is the most sensitive quantity to reflect small variations of the timing properties that are caused by magnetic field rearrangements. Methods. We performed axisymmetric, long-term simulations of the magneto-thermal evolution of neutron stars with state-of-the-art microphysical inputs to calculate the evolution of the braking index. Relatively rapid magnetic field modifications can be expected only in the crust of neutron stars, where we focus our study. Results. We find that the effect of the magnetic field evolution on the braking index can be divided into three qualitatively different stages depending on the age and the internal temperature: a first stage that may be different for standard pulsars (with n � 3) or low field neutron stars that accreted fallback matter during the supernova explosion (systematically n < 3); in a second stage, the evolution is governed by almost pure Ohmic field decay, and a braking index n > 3 is expected; in the third stage, at late times, when the interior temperature has dropped to very low values, Hall oscillatory modes in the neutron star crust result in braking indices of a high absolute value and both positive and negative signs. Conclusions. Current magneto-thermal evolution models predict a large contribution to the timing noise and, in particular, to the braking index, from temporal variations of the magnetic field. Models with strong (�1014 G) multipolar or toroidal components, even with a weak (�1012 G) dipolar field are consistent with the observed trend of the timing properties.

Item URL in elib:https://elib.dlr.de/79733/
Document Type:Article
Title:Pulsar Timing irregularities and the imprint of magnetic field evolution
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Pons, Josejose.pons (at) ua.esUNSPECIFIED
Viganno, Danieledaniele.vigano (at) ua.esUNSPECIFIED
Geppert, Ulrichulrich.geppert (at) dlr.deUNSPECIFIED
Date:November 2012
Journal or Publication Title:Astronomy and Astrophysics
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:547
DOI :10.1051/0004-6361/201220091
Publisher:EDP Sciences
Status:Published
Keywords:pulsars: general � stars: neutron � stars: magnetic field � stars: evolution
HGF - Research field:other
HGF - Program:other
HGF - Program Themes:other
DLR - Research area:no assignment
DLR - Program:no assignment
DLR - Research theme (Project):no assignment
Location: Bremen
Institutes and Institutions:Institute of Space Systems > Systemkonditionierung
Deposited By: Geppert, Prof. Dr.rer.nat. habil. Ulrich
Deposited On:30 Jan 2013 09:10
Last Modified:08 Mar 2018 18:54

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