We report on a survey for H \alpha bow shock emission around nearby \gamma -detected energetic pulsars .
This survey adds three Balmer-dominated neutron star bow shocks to the six previously confirmed examples .
In addition to the shock around Fermi pulsar PSR J1741 - 2054 , we now report H \alpha structures around two additional \gamma -ray pulsars , PSR J2030+4415 and PSR J1509 - 5850 .
These are the first known examples of H \alpha nebulae with pre-ionization halos .
With new measurements , we show that a simple analytic model can account for the angular size and flux of the bow shocks ’ apices .
The latter , in particular , provides a new pulsar probe and indicates large moments of inertia and smaller distances than previously assumed , in several cases .
In particular we show that the re-measured PSR J0437 - 4715 shock flux implies I = ( 1.7 \pm 0.2 ) \times 10 ^ { 45 } / ( f _ { HI } { sin } i ) { g cm ^ { 2 } } .
We also derive a distance d \approx 0.72 kpc for the \gamma -ray only pulsar PSR J2030+4415 and revised distances for PSRs J1959+2048 ( 1.4 kpc ) and J2555+6535 ( \sim 1 kpc ) , smaller than the conventional DM-estimated values .
Finally we report upper limits for 94 additional LAT pulsars .
An estimate of the survey sensitivity indicates that for a warm neutral medium filling factor \phi _ { WNM } \sim 0.3 there should be a total of \sim nine H \alpha bow shocks in our LAT-targeted survey ; given that seven such objects are now known , a much larger \phi _ { WNM } seems problematic .