2008A&A...488.1027M

The multi-wavelength study of old (>100Myr) radio pulsars holds the key to understanding the long-term evolution of neutron stars, including the advanced stages of neutron star cooling and the evolution of the magnetosphere. Optical/UV observations are particularly useful for such studies because they allow one to explore both thermal and non-thermal emission processes. In particular, studying the optical/UV emission constrains the temperature of the bulk of the neutron star surface, too cold to be measured in X-ray observations. Aim of this work is to identify the optical counterpart of the very old (166Myr) radio pulsar J0108-1431.We have re-analyzed our original Very Large Telescope (VLT) observations, where a very faint object was tentatively detected close to the radio position, near the edge of a field galaxy.We found that the backward extrapolation of the PSR J0108-1431 proper motion recently measured by Chandra fits the position of this object. Based on that, we propose it as a viable candidate for the optical counterpart to PSR J0108-1431. The object fluxes (U=26.4±0.3; B≃27.9; V≥27.8) are consistent with a thermal spectrum with a brightness temperature of ∼9x10⁴K (for R=13km at a distance of 130pc), emitted from the bulk of the neutron star surface. New optical observations are required to confirm the optical identification of PSR J0108-1431 and measure its spectrum.