The role of multipolar magnetic fields in pulsar magnetospheres |
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| Authors: | Estelle Asseo David Khechinashvili |
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| Institution: | Centre de Physique Théorique, Ecole Polytechnique, 91128 Palaiseau CEDEX, France; Institute of Astronomy, University of Zielona Góra, Lubuska 2, 65-265 Zielona Góra, Poland; Center of Plasma Astrophysics, Abastumani Astrophysical Observatory, Al. Kazbegi Avenue 2a, 380060 Tbilisi, Georgia |
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| Abstract: | We explore the role of complex multipolar magnetic fields in determining physical processes near the surface of rotation powered pulsars. We model the actual magnetic field as the sum of global dipolar and star-centred multipolar fields. In configurations involving axisymmetric and uniform multipolar fields, 'neutral points' and 'neutral lines' exist close to the stellar surface. Also, the curvature radii of magnetic field lines near the stellar surface can never be smaller than the stellar radius, even for very high-order multipoles. Consequently, such configurations are unable to provide an efficient pair-creation process above pulsar polar caps, necessary for plasma mechanisms of generation of pulsar radiation. In configurations involving axisymmetric and non-uniform multipoles, the periphery of the pulsar polar cap becomes fragmented into symmetrically distributed narrow subregions where curvature radii of complex magnetic field lines are less than the radius of the star. The pair-production process is only possible just above these 'favourable' subregions. As a result, the pair plasma flow is confined within narrow filaments regularly distributed around the margin of the open magnetic flux tube. Such a magnetic topology allows us to model the system of 20 isolated subbeams observed in PSR B0943+10 by Deshpande & Rankin. We suggest a physical mechanism for the generation of pulsar radio emission in the ensemble of finite subbeams, based on specific instabilities. We propose an explanation for the subpulse drift phenomenon observed in some long-period pulsars. |
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| Keywords: | instabilities magnetic fields plasmas waves pulsars: general |
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