Constraining the Spin-Down of the Nearby Isolated Neutron Star RX J2143.0+0654

Magnetic field estimates for nearby isolated neutron stars (INS) help to constrain both the characteristics of the population and the nature of their peculiar X-ray spectra. From a series of XMM -Newton observations of RX J2143.0+0654, we measure a spin-down rate of \dot{ν}= {(-4.6± 2.0) × 10^{-16}} Hz s^{-1}. While this does not allow a definitive measurement of the dipole magnetic field strength, fields of gsim10¹⁴ G such as those inferred from the presence of a spectral absorption feature at 0.75 keV are excluded. Instead, the field is most likely around 2 × 10¹³ G, very similar to those of other INS. We not only suggest that this similarity most likely reflects the influence of magnetic field decay on this population, but also discuss a more speculative possibility that it results from peculiar conditions on the neutron-star surface. We find no evidence for spectral variability above the ~2% level. We confirm the presence of the 0.75 keV feature found earlier, and find tentative evidence for an additional absorption feature at 0.4 keV.