  The highest brightness temperature ever observed are from "nanoshots" from
the Crab pulsar which we argue could be the signature of bursts of vacuum
$e^{\pm}$ pair production. If so this would be the first time the astronomical
Schwinger effect has been observed. These "Schwinger sparks" would be an
intermittent but extremely powerful, $\sim 10^3 L_{\astrosun}$, 10 PeV
$e^{\pm}$ accelerator in the heart of the Crab. These nanosecond duration
sparks are generated in a volume less than $1 m^3$ and the existence of such
sparks has implications for the small scale structure of the magnetic field of
young pulsars such as the Crab. This mechanism may also play a role in
producing other enigmatic bright short radio transients such as fast radio
bursts.
