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arXiv · 2501.04768

From proto-neutron star dynamo to low-field magnetars

Andrei Igoshev·Paul Barrère·Raphaël Raynaud·Jérome Guilet·Toby Wood·Rainer Hollerbach
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Abstract

Low-field magnetars have dipolar magnetic fields that are 10-100 times weaker than the threshold, $B \gtrsim 10^{14}$ G, used to define classical magnetars, yet they produce similar X-ray bursts and outbursts. Using the first direct numerical simulations of magneto-thermal evolution starting from a dynamo-generated magnetic field, we show that the low-field magnetars can be produced as a result of a Tayler--Spruit dynamo inside the proto-neutron star. We find that these simulations naturally explain key characteristics of low-field magnetars: (1) weak ($\lesssim 10^{13}$ G) dipolar magnetic fields, (2) strong small-scale fields, and (3) magnetically induced crustal failures producing X-ray bursts. These findings suggest two distinct formation channels for classical and low-field magnetars, potentially linked to different dynamo mechanisms.

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Andrei Igoshev, Paul Barrère, Raphaël Raynaud, Jérome Guilet, Toby Wood, Rainer Hollerbach. 2025-01-08. From proto-neutron star dynamo to low-field magnetars. https://arxiv.org/abs/2501.04768

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