The intrinsic intensity modulation of PSR B1937+21 at 1410 MHz

The single- pulse properties of the millisecond radio pulsar PSR B1937 + 21 are studied at 1410 MHz. The nongiant pulse emission regions appear to be remarkably stable, showing no pulse- to- pulse fluctuations other then those induced by the interstellar medium. This type of behavior has not been seen in any other pulsar, although it was seen in previous 430 MHz observations of this source. The stability of this source is interpreted in the context of the sparking gap model of radio pulsar emission, and a model- dependent upper bound is placed on the Lorentz factor of the outflowing plasma.