GEMINGA IN THE SPACE TELESCOPE ERA

The distance to Geminga inferred from the gamma-ray flux, the interste llar absorption of the soft X-ray emission and the proper motion measu red for its optical counterpart, range from tens of parsecs to an uppe r limit of severl hundreds of parsecs. These distance estimates, howev er, are based on a number of assumptions on the emission mechanisms, o n the structure of the interstellar medium and on the intrinsic speed of this neutron star. The refurbished Hubble Space Telescope offers, f or the first time, the possibility to assess directly the distance to Geminga through the measure of the annual parallactic displacement of the optical counterpart G ''. The resulting value is 157(-34)(+59) pc. The repeated precise positioning of G '' yielded also, as a by produc t, a very accurate measure of its proper motion.