Keywords

The coupled evolution of pulsar rotation and inclination angle in the wind braking model is calculated. The oblique pulsar tends to align. The pulsar alignment affects its spin-down behavior. As a pulsar evolves from the magneto-dipole radiation dominated case to the particle wind dominated case, the braking index first increases and then decreases. In the early time, the braking index may be larger than three. During the following long time, the braking index is always smaller than three. The minimum braking index is about one. This can explain the existence of a high braking index larger than three and a low braking index simultaneously. The pulsar braking index is expected to evolve from larger than three to about one. The general trend is for the pulsar braking index to evolve from the Crab-like case to the Vela-like case.

We report the discovery of a 206 ms pulsar associated with the TeV γ-ray source HESS J1640−465 using the Nuclear Spectroscopic Telescope Array (NuSTAR) X-ray observatory. PSR J1640−4631 lies within the shell-type supernova remnant (SNR) G338.3−0.0, and coincides with an X-ray point source and putative pulsar wind nebula (PWN) previously identified in XMM-Newton and Chandra images. It is spinning down rapidly with period derivative $\dot{P} =$ 9.758(44) × 10⁻¹³, yielding a spin-down luminosity $\dot{E} =$ 4.4 × 10³⁶ erg s⁻¹, characteristic age $\tau _c \equiv P/2\dot{P} =$ 3350 yr, and surface dipole magnetic field strength B_s = 1.4 × 10¹³ G. For the measured distance of 12 kpc to G338.3−0.0, the 0.2–10 TeV luminosity of HESS J1640−465 is 6% of the pulsar's present $\dot{E}$. The Fermi source 1FHL J1640.5−4634 is marginally coincident with PSR J1640−4631, but we find no γ-ray pulsations in a search using five years of Fermi Large Area Telescope (LAT) data. The pulsar energetics support an evolutionary PWN model for the broadband spectrum of HESS J1640−465, provided that the pulsar's braking index is n ≈ 2, and that its initial spin period was P₀ ∼ 15 ms.