Spin period evolution and x-ray spectral characteristics of the Small Magellanic Cloud pulsar SXP 46.6

We characterize the Small Magellanic Cloud pulsar SXP 46.6 using NuSTAR observations conducted in 2017. The spin period ($P$) of this neutron star decreased from its discovered value of 46.6 s to a value of 45.984(1) s, indicating a spin-up at the rate of $\stackrel{\ifmmode \dot{}\else \textperiodcentered \fi{}}{P}=\ensuremath{-}1.13\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\text{ }\text{ }\mathrm{s}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$. This spin-up rate is used to calculate a high pulsar magnetic field value of $2.25\ifmmode\times\else\texttimes\fi{}{10}^{13}\text{ }\text{ }\mathrm{G}$. This process also gives a low magnetic field value, which we rule out here by constraining the inner accretion disk radius to be less than the radius of the innermost stable circular orbit. The pulse profile, analyzed in soft, hard, and broad x-ray bands, shows a double-peaked structure, consistent with pencil beam emission from two antipodal hot spots on the neutron star surface. We also perform spin phase-resolved spectroscopy for the first time, revealing spectral variations across different phases of the pulsar's rotation. These results offer new insights into the long-term spin evolution and emission properties of SXP 46.6.