We have detected a strong deflection of radio waves from the pulsar PSR B0834+06 in scintillation observations .
Interference between the undeflected pulsar image and deflected subimages allows single dish interferometry of the interstellar medium with sub-milliarcsecond resolution .
We infer the presence of scattering structure ( s ) similar to those that are thought to cause Extreme Scattering Events in quasar flux monitoring programs : size \sim 0.2 \textrm { AU } ( an angular size of 0.1 \textrm { mas } ) with an electron overdensity of \gtrsim 10 ^ { 3 } compared to the warm ionized medium .
The deflectors are nearly stationary in a scattering screen that is thin ( \lesssim 5 \% of the pulsar-observer distance in extent ) , is located 70 \% of the way from the Earth to the pulsar , and has been seen consistently in observations dating back 20 years .
The pulsar scans the scattering screen at a velocity of 110 \textrm { km s } ^ { -1 } with a detection radius of 15 \textrm { mas } .
Pulsar observations such as these — particularly with a new generation of low-frequency radio telescopes with large collecting areas — hold promise for improving constraints on the poorly understood physical characteristics and space density of the deflecting structures .
Such observations may also prove useful in correcting deviations the deflectors produce in high-precision timing of millisecond pulsars .