SIMBAD references

We present optical data which suggests that G", the optical counterpart of the γ-ray pulsar Geminga, possibly pulses in B with a period of 0.237 seconds. The similarity between the optical pulse shape and the γ-ray light curve indicates that a large fraction of the optical emission is non-thermal in origin - contrary to recent suggestions based upon the total optical flux. The derived magnitude of the pulsed emission is m_B=26.0±0.4. Whilst it is not possible to give an accurate figure for the pulsed fraction (due to variations in the sky background) we can give an 1σ upper limit of m_B≃27 for the unpulsed fraction.