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arXiv · 1404.3705

Possible Evidence for Free Precession of a Strongly Magnetized Neutron Star in the Magnetar 4U 0142+61

Kazuo Makishima·Teruaki Enoto·Junko S. Hiraga·Toshio Nakano·Kazuhiro Nakazawa·Soki Sakurai·Makoto Sasano·Hiroaki Murakami
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Abstract

Magnetars are a special type of neutron stars, considered to have extreme dipole magnetic fields reaching ~1e+11 T. The magnetar 4U 0142+61, one of prototypes of this class, was studied in broadband X-rays (0.5-70 keV) with the Suzaku observatory. In hard X-rays (15-40 keV), its 8.69 sec pulsations suffered slow phase modulations by +/-0.7 sec, with a period of ~15 hours. When this effect is interpreted as free precession of the neutron star, the object is inferred to deviate from spherical symmetry by ~1.6e-4 in its moments of inertia. This deformation, when ascribed to magnetic pressure, suggests a strong toroidal magnetic field, ~1e+12 T, residing inside the object. This provides one of the first observational approaches towards toroidal magnetic fields of magnetars.

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Kazuo Makishima, Teruaki Enoto, Junko S. Hiraga, Toshio Nakano, Kazuhiro Nakazawa, Soki Sakurai, Makoto Sasano, Hiroaki Murakami. 2014-04-20. Possible Evidence for Free Precession of a Strongly Magnetized Neutron Star in the Magnetar 4U 0142+61. https://doi.org/10.1103/physrevlett.112.171102

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