Magnetic field topology in pulsars

Abstract

It is shown that the location of the spin-up line in the P-P˙ diagram is sensitive to the presence of large-scale magnetic anomalies (quadrupole,...) and that one can usefully constrain the surface strength of such fields to be not more than ∼40% of the surface strength of the dipole in spun-up pulsars. This constraint shows that if gamma-ray bursters are related to old Galactic neutron stars, those with strong cyclotron lines cannot have had the same magnetic history as spun-up millisecond pulsars. The spin-up line also constrains models in which the magnetic field is a single intense surface pole, although the present data set has too few very short period pulsars with measured P˙ to provide useful information