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Astron. Astrophys. 342, L5-L8 (1999)

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Letter to the Editor

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

A. Golden 1 and A. Shearer 2

1 Department of Physics, National University of Ireland, Galway, Ireland
2 Information Technology Centre, National University of Ireland, Galway, Ireland

Received 2 October 1998 / Accepted 10 December 1998


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 [FORMULA] parameter. For Geminga, with a known distance of [FORMULA] 160 pc, we find that [FORMULA] [FORMULA] 9.5 km for a [FORMULA] blackbody source, and [FORMULA] [FORMULA] 10.0 km with the presence of a magnetized H atmosphere. In addition, we suggest that PSR B0656+14 is some [FORMULA] 4-5 times closer than the 760 pc estimated from DM measurements alone.

Key words: stars: pulsars: individual: Geminga, PSR B0656+14

Send offprint requests to: A. Golden (agolden@physics.ucg.ie)

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© European Southern Observatory (ESO) 1999

Online publication: December 22, 1998