http://arxiv.org/abs/2108.01051
A fraction of young neutron stars, magnetars, have ultra-strong magnetic fields. Models invoked for their strong fields require highly specific conditions with extreme parameters which are incompatible with the inference that the magnetar birth rate is comparable to the rate of core-collapse supernovae. We suggest that these seemingly contradictory trends can be reconciled if the PNS dynamo generates oscillating toroidal fields towards the end of the dynamo action. Such oscillations are ubiquitous in dynamo models. Depending on the phase of the oscillation at which the dynamo process terminates, the neutron star can have a very high or relatively small toroidal field. As an example, we invoke a shear-driven dynamo model for the generation of PNS magnetic fields. We show that the toroidal field oscillates as a harmonic oscillator while the poloidal field saturates. We argue that the same dynamo action can lead to the formation of both magnetars and ordinary neutron stars depending on at what phase of the oscillation the fields froze.
&. Bakır and K. Ekşi
Tue, 3 Aug 21
9/90
Comments: 5 pages, 1 figure and supplementary material