Radius and distance estimates of the isolated neutron stars Geminga and PSR B0656+14 using optical photometry

Integrated ground-based and HST optical studies of isolated neutron stars have provided important independent datasets in the determination of emission activity, particularly in the fitting of anticipated Rayleigh-Jeans extrapolations from EUV soft X-ray datasets, despite their intrinsic faintness. Differentiation of the pulsed and unpulsed fluxes and consequently of the nonthermal and thermal modes of emission could provide definitive data with which to constrain this blackbody continuum. Based upon high speed photometric observations of Geminga and PSR B0656+14 in the B band, we have combined upper limits of unpulsed emission with recently published model-fits with a view to assessing possible implications for the Rid parameter. For Geminga, with a known distance of similar to 160 pc, we find that R-infinity less than or equal to 9.5 km for a similar to blackbody source, and R-infinity less than or equal to 10.0 km with the presence of a magnetized H atmosphere. In addition, we suggest that PSR B0656+14 is some similar to 4-5 times closer than the 760 pc estimated from DM measurements alone.