General solution for the vacuum electromagnetic field in the surroundings of a rotating star

S. Bonazzola (1) , F. Mottez (1) , J. Heyvaerts (2)

1 LUTH (UMR_8102) - Laboratoire Univers et Théories
2 ObAS - Observatoire astronomique de Strasbourg

Aims. Many recent observations of pulsars and magnetars can be interpreted in terms of neutron stars (NS) with multipole electromagnetic fields. As a first approximation, we investigate the multipole magnetic and electric fields in the environment of a rotating star when this environment is deprived of plasma. Methods. We compute a multipole expansion of the electromagnetic field in vacuum for a given magnetic field on the conducting surface of the rotating star. Then, we consider a few consequences of multipole fields of pulsars. Results. We provide an explicit form of the solution. For each spherical harmonic of the magnetic field, the expansion contains a finite number of terms. A multipole magnetic field can provide an explanation for the stable sub-structures of pulses, and they offer a solution to the problem of current closure in pulsar magnetospheres. Conclusions. This computation generalises the widely used model of a rotating star in vacuum with a dipole field. It can be especially useful as a first approximation to the electromagnetic environment of a compact star, for instance a neutron star, with an arbitrarily magnetic field.

Mots clés: Pulsars; Multipoles; Electromagnetic Fields

Domaines: Phénomènes cosmiques de haute energie [astro-ph.HE]

S. Bonazzola, F. Mottez, J. Heyvaerts. General solution for the vacuum electromagnetic field in the surroundings of a rotating star. 2014. ⟨hal-01078950⟩