Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Magnetic Axis Drift and Magnetic Spot Formation in Neutron Stars with
  Toroidal Fields   We explore magnetic field configurations that lead to the formation of
magnetic spots on the surface of neutron stars, and to 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 $0.4^{\circ}$ 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 $P-\dot{P}$
diagram and the observational implications. We find that neutron stars spend a
very short time before they cross the Death-Line of the $P-\dot{P}$ 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
behaviour, having a weak dipole field, yet hosting a magnetic spot responsible
for its magnetar behaviour. 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.

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The categories of this paper are: ao-sci
11
The categories of this paper are: hep-lat
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The categories of this paper are: math-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: adap-org
15
The categories of this paper are: nucl-ex
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The categories of this paper are: funct-an
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The categories of this paper are: dg-ga
4
The categories of this paper are: cond-mat
0
The categories of this paper are: hep-ph
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The categories of this paper are: q-fin
9
The categories of this paper are: nlin
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The categories of this paper are: acc-phys
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The categories of this paper are: hep-th
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The categories of this paper are: q-bio
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The categories of this paper are: plasm-ph