Magnetic fields and spin periods of observed pulsars, where data are taken from the ATNF pulsar catalogue. Black dots are normal pulsars. Red dots represent MSPs. Green triangles are pulsars in binaries. The “spin-up line” represents the minimum spin-period to which a spin-up process may proceed in an Eddington-limited accretion, while the “death-line” corresponds to a polar cap voltage below which the pulsar activity is likely to switch off (Bhattacharya & van den Heuvel 1991).