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Spin-down changes in PSR B0540-69 induced by a drift of the magnetic axis

Lucas G. Barão, J. E. Horvath

TL;DR

The paper addresses why pulsar braking indices deviate from the ideal $n=3$ dipole model by proposing a crustal platelet tectonics mechanism that slowly drifts the magnetic axis and reconfigures the magnetosphere, coupling interior dynamics to external torques. It analyzes PSR B0540-69, showing a 2011 spin-down-rate transition without a frequency jump but with a large change in $\dot{\nu}$ and an increase in PWN luminosity, which the authors interpret as a permanent tilt $\Delta\chi \approx 8^\circ$ that enhances the wind torque. The braking-index evolution is modeled with a Kohlrausch–Williams–Watts form for the tilt rate $\dot{\chi}(t)$, yielding a consistent set of parameters including $B \approx 4.17\times 10^{13}$ G and $L_p \approx 7.45\times 10^{38}$ erg s$^{-1}$, and explaining the long-term $n$-trajectory from near zero toward $\sim$1.4. The study generalizes the scenario to other SRT-like events, emphasizing crust–magnetosphere coupling as a framework for abrupt torque changes and motivating future observations to test these predictions.

Abstract

The dynamics of the solid crust + magnetic field lines of pulsars is a much debated issue, and remains unsettled after 50 years. Some pieces of evidence have emerged to complete and confirm theoretical calculations and expectations. We discuss in the present work an interpretation of the behavior of the ''Crab Twin'' pulsar PSR B0540-69 in terms of the evolution of the magnetic field/quakes, connecting the behavior of the braking index with the underlying platelet drift and sudden discontinuous rearrangement (fast-slip) and long-term ones (slow-slip events), suggested by analogy with existing theoretical picture observed in the Earth's crust. The relationship of this scenario with permanent torque-changing glitches seen in the Crab and other young pulsars, and a set of similar events in the same object and others is addressed. We conclude that this physical approach is in principle consistent with all these sudden events, and point out future work to clarify the whole picture.

Spin-down changes in PSR B0540-69 induced by a drift of the magnetic axis

TL;DR

The paper addresses why pulsar braking indices deviate from the ideal dipole model by proposing a crustal platelet tectonics mechanism that slowly drifts the magnetic axis and reconfigures the magnetosphere, coupling interior dynamics to external torques. It analyzes PSR B0540-69, showing a 2011 spin-down-rate transition without a frequency jump but with a large change in and an increase in PWN luminosity, which the authors interpret as a permanent tilt that enhances the wind torque. The braking-index evolution is modeled with a Kohlrausch–Williams–Watts form for the tilt rate , yielding a consistent set of parameters including G and erg s, and explaining the long-term -trajectory from near zero toward 1.4. The study generalizes the scenario to other SRT-like events, emphasizing crust–magnetosphere coupling as a framework for abrupt torque changes and motivating future observations to test these predictions.

Abstract

The dynamics of the solid crust + magnetic field lines of pulsars is a much debated issue, and remains unsettled after 50 years. Some pieces of evidence have emerged to complete and confirm theoretical calculations and expectations. We discuss in the present work an interpretation of the behavior of the ''Crab Twin'' pulsar PSR B0540-69 in terms of the evolution of the magnetic field/quakes, connecting the behavior of the braking index with the underlying platelet drift and sudden discontinuous rearrangement (fast-slip) and long-term ones (slow-slip events), suggested by analogy with existing theoretical picture observed in the Earth's crust. The relationship of this scenario with permanent torque-changing glitches seen in the Crab and other young pulsars, and a set of similar events in the same object and others is addressed. We conclude that this physical approach is in principle consistent with all these sudden events, and point out future work to clarify the whole picture.
Paper Structure (6 sections, 9 equations, 2 figures, 2 tables)

This paper contains 6 sections, 9 equations, 2 figures, 2 tables.

Table of Contents

  1. Introduction
  2. The behavior of PSR B0540-69
  3. Possible changes in the shape of the pulse following the event
  4. The braking index post-SRT11
  5. Other similar events
  6. Discussion and Conclusions

Figures (2)

  • Figure 1: The jump of the X-ray luminosity detected by NuSTAR and Swift XRT related to the event of 2011. Blue lines indicate the central average values before and after the event. Note that besides its slow rise, the higher value stabilizes, arguing in favor of a permanent change in the PWN energy budget.
  • Figure 2: The best fit to the evolution of the braking index between the SRT11 time and 2019, using Equation \ref{['eq:phenom']}. The reduced chi-squared is $\chi_{\rm{red}}=1.87$.