Authors: Toropina O.D., Romanova M.M. and Lovelace R. V. E.  

We use axisymmetric magnetohydrodynamic simulations to investigate the spinning-down of magnetars rotating in the propeller regime and moving supersonically through the interstellar medium. The simulations indicate that magnetars spin-down rapidly due to this interaction, faster than for the case of a non-moving star. From many simulation runs we have derived an approximate scaling laws for the angular momentum loss rate: 
dL/dt ~ -
hm0.3 m0.6 r0.8 M-0.4 W*1.5, where r is the density of the interstellar medium, M is Mach number, m is the star's magnetic moment, W* is its angular velocity, and hm is magnetic diffusivity. A magnetar with a surface magnetic field of 1013 - 1015 G is found to spin-down to a period P > 105 - 106 s in ~ 104 -105 years. There is however uncertainty about the value of the magnetic diŽusivity so that the time-scale may be longer. We discuss this model in respect of Soft Gamma Repeaters (SGRs) and the isolated neutron star candidate RXJ1856.5-3754.

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Last updated on 29.01.07