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 { \nu } = ( -4.6 \pm 2.0 ) \times 10 ^ { -16 } { Hz } { s } ^ { -1 } .
While this does not allow a definitive measurement of the dipole magnetic field strength , fields of \gtrsim 10 ^ { 14 } 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 \times 10 ^ { 13 } 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 \sim 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 .