PSR B1951+32 and PSR J0537-6910 - where are the optical counterparts?
  There remain several definitive gamma-ray pulsars that are as yet undetected in the optical regime. A classic case is the pulsar PSR B1951+32, associated with the complex CTB 80 SNR. Previous ground based high speed 2-d optical studies have ruled out candidates to m_V ~ 24. Hester (2000) has reported an analysis of archival HST/WFPC2 observations of the CTB 80 complex which suggest a compact synchrotron nebula coincident with the pulsar's radio position. Performing a similar analysis, we have identified a possible optical counterpart within this synchrotron nebula at m_V ~ 25.5, and another optical counterpart candidate nearby at m_V ~ 24.2.   PSR J0537-6910 is a young (canonical age ~ 5000 years), 16ms pulsar in the LMC. We report a search for optical pulsations from the region around the X-ray position. We see no obvious candidate exhibiting optical pulsations at the X-ray period, with a 3 sigma upper limit of m_V ~ 23.6. We have also examined recent Chandra results (Wang et al. 2001) and show that their X-ray-Optical astrometry is in error by about 7''. 
R. F. Butler (National University of Ireland, Galway), A. Golden   (National University of Ireland, Galway), A. Shearer (Nat...