paper

The Early Evolution of Magnetar Rotation I: Slowly Rotating "Normal" Magnetars

arXiv:2208.09042 · doi:10.1093/mnras/stac2651

Abstract

In the seconds following their formation in core-collapse supernovae, "proto"-magnetars drive neutrino-heated magneto-centrifugal winds. Using a suite of two-dimensional axisymmetric MHD simulations, we show that relatively slowly rotating magnetars with initial spin periods of ms spin down rapidly during the neutrino Kelvin-Helmholtz cooling epoch. These initial spin periods are representative of those inferred for normal Galactic pulsars, and much slower than those invoked for gamma-ray bursts and super-luminous supernovae. Since the flow is non-relativistic at early times, and because the Alfvén radius is much larger than the proto-magnetar radius, spindown is millions of times more efficient than the typically-used dipole formula. Quasi-periodic plasmoid ejections from the closed zone enhance spindown. For polar magnetic field strengths G, the spindown timescale can be shorter than than the Kelvin-Helmholtz timescale. For G, it is of order seconds in early phases. We compute the spin evolution for cooling proto-magnetars as a function of , , and mass (). Proto-magnetars born with greater than spin down to periods s in just the first few seconds of evolution, well before the end of the cooling epoch and the onset of classic dipole spindown. Spindown is more efficient for lower and for larger . We discuss the implications for observed magnetars, including the discrepancy between their characteristic ages and supernova remnant ages. Finally, we speculate on the origin of 1E 161348-5055 in the remnant RCW 103, and the potential for other ultra-slowly rotating magnetars.

arXiv comment16 pages, 10 figures

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