Parallax Observations with the [ITAL]Hubble Space Telescope[/ITAL] Yield the Distance to Geminga

Abstract

Using data from Hubble Space Telescope observations, we report the first optical measurement of the annual parallax of a neutron star. This is the counterpart of the X-ray/ gamma -ray pulsar Geminga, for which strong proper motion has already been reported. Significant displacement from such motion is detected using WFPC2 observations, taken at the dates of the maximum predicted parallactic factor. The resulting distance value is 157 pc (+59, -34), just consistent with the lower end of the wide range derived from X-ray data. This measurement solves the long-standing problem of Geminga's distance and allows for the first precise determination of a neutron star luminosity from electron volts to giga--electron volts. Moreover, the repeated precise positionings substantially improve our knowledge of its proper motion.