A possible optical counterpart to the old nearby pulsar J0108-1431 ^*

¹ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK e-mail: rm2@mssl.ucl.ac.uk
² Department of Astronomy and Astrophysics, Pennsylvania State University, PA 16802, USA e-mail: pavlov@astro.psu.edu
³ Department of Astronomy, University of Florida, 32611, USA e-mail: oyk100@astro.ufl.edu

Received: 16 May 2008
Accepted: 1 July 2008

Abstract

Context. The multi-wavelength study of old (>100 Myr) 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.

Aims. Aim of this work is to identify the optical counterpart of the very old (166 Myr) radio pulsar J0108-1431.

Methods. 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.

Results. 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 (; ; ) are consistent with a thermal spectrum with a brightness temperature of ∼ K (for  km at a distance of 130 pc), emitted from the bulk of the neutron star surface.

Conclusions. New optical observations are required to confirm the optical identification of PSR J0108-1431 and measure its spectrum.