UVOIR Spectrum, X-Ray Emission, and Proper Motion of the Isolated Neutron Star RX J2143.0+0654

We observed the isolated neutron star (NS) RX J2143.0+0654 with the Hubble Space Telescope (HST) in the UVOIR wavelength range (0.14-1.7 μm). The UV part is consistent with a Rayleigh-Jeans tail of a thermal spectrum, f_ν ∝ ν², while a power-law spectrum, f_ν ∝ ν^α with α ∼ −0.8, dominates in the near-IR-optical. A joint fit of the UVOIR and contemporaneous X-ray spectra with a two-component blackbody with possible absorption features + power-law optical spectrum yields the following temperature and apparent radius of the colder component (which gives the main contribution in the UV): kT_cold ≈ 45 eV and R_cold ≈ 6d₂₆₀ km, where d₂₆₀ is the distance in units of 260 pc. The temperature and radius of the hotter component, kT_hot ≈ 106 eV and R_hot ≈ 1.5d₂₆₀ km; the parameters of an absorption feature at 0.74 keV; and the properties of X-ray pulsations are the same as found in previous X-ray observations. In the near-IR images, the NS is possibly surrounded by extended emission with a characteristic size of ∼2″ and flux densities of about 1.7 and 0.9 μJy at 1.54 and 1.15 μm, respectively. Comparison with a previous HST observation in the optical 14 yr ago shows a proper motion μ ≈ 6 mas yr⁻¹, which corresponds to a small transverse velocity of 7d₂₆₀ km s⁻¹. It is consistent with the hypothesis that the NS was born in the vicinity of the solar system about 0.5 Myr ago.