Abstract X-ray dim isolated neutron stars are peculiar pulsar-like objects, characterized by their Planck-like spectrum. In studying their spectral energy distributions, optical/ultraviolet (UV) excess is a long standing problem. Recently Kaplan et al. measured the optical/UV excess for all seven sources, which is understandable in the resonant cyclotron scattering (RCS) model previously addressed. The RCS model calculations show that the RCS process can account for the observed optical/UV excess for most sources. The flat spectrum of RX J2143.0+0654 may be due to contributions from the bremsstrahlung emission of the electron system in addition to the RCS process.

Keywords pulsars: individual (RX J0420.0–5022, RX J0720.4–3125, RX J0806.4– 4123, RX J1308.6+2127, RX J1605.3+3249, RX J1856.5–3754, RX J2143.0+0654) — stars: neutron

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