Late-blooming magnetars: awakening as long period transients after a dormant cooling epoch

TL;DR

This paper proposes a magnetothermal model explaining how dormant neutron stars can become active magnetars with long periods and radio emissions after a cooling epoch, suggesting a new evolutionary pathway.

Contribution

It introduces a model where electric currents in the core lead to late activation of magnetar activity, distinct from known classes.

Findings

Neutron stars remain silent for ~0.1 Myr during cooling.

Magnetic evolution triggers crustal failures and radio pulsing.

Late-blooming magnetars form a separate evolutionary branch.

Abstract

Long-period transients are an elusive class of compact objects uncovered by radio surveys. While magnetars are a leading candidate for those sources that appear isolated, several observational properties challenge the established evolutionary framework: (i) low quiescent X-ray luminosities, (ii) $\sim$hour-long rotational periods, and (iii) highly-variable radio flux. It is shown via magnetothermal modelling that, if electric currents thread the fluid core at the time of crust freezing, the neutron star remains multiband silent for an initial period of approximately 0.1 Myr while cooling passively. Once the crust becomes cold enough, the Hall effect begins to dominate the magnetic evolution, triggering crustal failures that inject magnetospheric twist that initiates radio pulsing while depleting rotational kinetic energy from an already-slow star. Depending on where electric currents circulate, such 'late-blooming' magnetars manifesting as long-period transients may thus form a distinct branch from soft gamma repeaters and anomalous X-ray pulsars.