A Possible Mechanism for the Origin of Ultrastrong Magnetic Field of Magnetars

Growing observations reveal that soft gamma-ray repeaters and anomalous x-ray pulsars are magnetars. Their magnetic fields may achieve 10¹⁴-10¹⁵G. We explore the origin of the superstrong magnetic field by considering the magnetization of the ³P₂ superfluid neutrons inside neutron stars (NSs). By solving the Tolman--Oppenheimer--Volkov equations together with the equation of state adopted by Elgaroy it et al. Phys. Rev. Lett. 77(1996)1428 in the calculation of the neutron pairing gap, we specifically calculate the NS internal structure, the permissible region for ³P₂ superfluid neutrons inside the NS, and the total magnetic moment contributed by the orderly arranged neutron vortexes. The result shows that the induced magnetic field may cover a wide range, which is consistent with the magnetic field predicted by the standard magnetic dipole radiation for pulsar spindown.