Evolution of proto-neutron stars to pulsars, magnetars and central compact objects

İrem Bakır; Kazım Yavuz Ekşi

doi:10.1093/mnras/stag051

paper

Evolution of proto-neutron stars to pulsars, magnetars and central compact objects

arXiv:2108.01051 · doi:10.1093/mnras/stag051

Abstract

Some young neutron stars, the magnetars, have ultra-strong magnetic fields, yet their inferred birth rate is comparable to the core-collapse supernova rate, challenging scenarios that require rare, extreme conditions. We propose that this discrepancy can be reconciled if both pulsars and magnetars pass through a dynamo process during the proto-neutron star (PNS) phase. We employ a shear-driven $α$ -- $Ω$ dynamo model that includes PNS contraction. The dynamo generically produces toroidal-dominated fields set mainly by the $Ω$ -effect. The evolution of the poloidal field is first dominated by flux conservation during collapse and then by the $α$ -effect. The saturated toroidal field depends strongly on the initial value of the shear, with a threshold at $q_{0} ≃ 0.23$ ; below this, the poloidal field remains near the value obtained by the flux-conservation ( $\approx 2.5 \times 1 0^{10} G$ ). For the shortest initial periods, the model leads to magnetar-like strengths ( $B_{p} ≃ 1 0^{15} G$ , $B_{ϕ} ≃ 1 0^{16} G$ ), while for the slower rotators it yields ordinary pulsar fields ( $B_{p} ≃ 1 0^{12} G$ , $B_{ϕ} ≃ 1 0^{14} G$ ). We also argue that the central compact objects can acquire toroidal fields amplified solely by the $Ω$ -effect; lacking the $α$ -effect, their poloidal fields are not shaped by the dynamo effect.

MNRAS accepted, 11 pages, 7 figures

Evolution of proto-neutron stars to pulsars, magnetars and central compact objects

Abstract

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