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Issue A&A
Volume 412, Number 2, December III 2003
Page(s) L33 - L36
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20034605



A&A 412, L33-L36 (2003)
DOI: 10.1051/0004-6361:20034605

Letter

Spot-like structures of neutron star surface magnetic fields

U. Geppert1, M. Rheinhardt1 and J. Gil1, 2

1  Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
2  Institute of Astronomy, University of Zielona Góra, Lubuska 2, 65-265 Zielona Góra, Poland

(Received 9 July 2003 / Accepted 3 November 2003)

Abstract
There is growing evidence, based on both X-ray and radio observations of isolated neutron stars, that besides the large-scale (dipolar) magnetic field, which determines the pulsar spin-down behaviour, small-scale poloidal field components are present, which have surface strengths one to two orders of magnitude larger than the dipolar component. We argue in this paper that the Hall-effect can be an efficient process in producing such small-scale field structures just above the neutron star surface. It is shown that due to a Hall-drift induced instability, poloidal magnetic field structures can be generated from strong subsurface toroidal fields, which are the result of either a dynamo or a thermoelectric instability acting at early times of a neutron star's life. The geometrical structure of these small-scale surface anomalies of the magnetic field resembles that of some types of "star-spots". The magnetic field strength and the length-scales are comparable with values that can be derived from various observations.


Key words: stars: neutron -- stars: pulsars -- stars: magnetic fields

Offprint request: U. Geppert, urme@aip.de

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