  Pulsars emit low-frequency radio waves through to high-energy gamma-rays that
are generated anywhere from the surface out to the edges of the magnetosphere.
Detecting correlated mode changes in the multi-wavelength emission is therefore
key to understanding the physical relationship between these emission sites.
Through simultaneous observations, we have detected synchronous switching in
the radio and X-ray emission properties of PSR B0943+10. When the pulsar is in
a sustained radio 'bright' mode, the X-rays show only an un-pulsed, non-thermal
component. Conversely, when the pulsar is in a radio 'quiet' mode, the X-ray
luminosity more than doubles and a 100%-pulsed thermal component is observed
along with the non-thermal component. This indicates rapid, global changes to
the conditions in the magnetosphere, which challenge all proposed pulsar
emission theories.
