Not an oxymoron: some X-ray binary pulsars with enormous spin-up rates reveal weak magnetic fields

作者：Christodoulou D M^*; Laycock S G T^*; Kazanas D^*

来源：Monthly Notices of the Royal Astronomical Society, 2018, 478(3): 3506-3512.

DOI：10.1093/mnras/sty1337

• accretion, accretion discs
• stars: neutron
• stars: pulsars: individual: SXP1062, SXP1323, NGC 300 ULX1
• magnetic fields
• X-rays: binaries

Three high-mass X-ray binaries have been discovered recently exhibiting enormous spin-up rates. Conventional accretion theory predicts extremely high-surface dipolar magnetic fields that we believe are unphysical. Instead, we propose quite the opposite scenario; some of these pulsars exhibit weak magnetic fields, so much so that their magnetospheres are crushed by the weight of inflowing matter. The enormous spin-up rate is achieved before inflowing matter reaches the pulsar's surface as the penetrating inner disc transfers its excess angular momentum to the receding magnetosphere, which, in turn, applies a powerful spin-up torque to the pulsar. This mechanism alsoworks in reverse; it spins a pulsar down when themagnetosphere expands beyond corotation and finds itself rotating faster than the accretion disc, which then exerts a powerful retarding torque to the magnetic field and to the pulsar itself. The above scenaria cannot be accommodated within the context of neutron-star accretion processes occurring near spin equilibrium, thus they constitute a step towards a new theory of extreme (far from equilibrium) accretion phenomena.

• 出版日期2018-8