We derive an upper limit of 3 mJy ( 95 % confidence ) for the flux density at 317 MHz of the Geminga pulsar ( J0633+1746 ) .
Our results are based on 7 hours of fast-sampled VLA data , which we averaged synchronously with the pulse period using a period model based on CGRO/EGRET gamma-ray data .
Our limit accounts for the fact that this pulsar is most likely subject to interstellar scintillations on a timescale much shorter than our observing span .
Our Bayesian method is quite general and can be applied to calculate the fluxes of other scintillated sources .
We also present a Bayesian technique for calculating the flux in a pulsed signal of unknown width and phase .
Comparing our upper limit of 3 mJy with the quoted flux density of Geminga at 102 MHz , we calculate a lower limit to its spectral index of \alpha \approx 2.7 ( F ( \nu ) \propto \nu ^ { - \alpha } ) .
We discuss some possible reasons for Geminga ’ s weakness at radio wavelengths , and the likelihood that many of the unidentified EGRET sources are also radio-quiet or radio-weak Geminga-like pulsars .