Novel Clues to the Physics of Magnetars as Probed with Detailed Pulse-Timing Studies

Broadband X-ray data of five magnetars show that their hard X-ray pulses suffer periodic phase modulations, at a period ∼ 10⁴ times their pulse period. The phenomenon is interpreted as a result of free precession of neutron stars that are prolately deformed to an asphericity of ∼ 10⁻⁴, by the magnetic stress of toroidal fields reaching ∼ 10¹⁶ G. The behavior is absent in their soft X-ray pulses, probably due to a higher emission symmetry. The ultra-high toroidal fields, considered common to magnetars, may persist longer than their dipole fields.