Using pulsar scintillation to probe AU-size structure in the interstellar medium

It is well known that pulsar dynamic spectra occasionally show pronounced fringing or criss-cross patterns. It was a surprise, however, that a two-dimensional Fourier analysis of these spectra showed faint, parabolic features, which are now called scintillation arcs. I will show evidence that the scintillation arc phenomenon is widespread and that it underpins many other scintillation phenomena. If an estimate of the distance to the pulsar and a measurement of its proper motion exist, then the location of the scattering material along the line of sight can be determined. There is often pronounced substructure in the arcs, and it translates along the main arc in a manner that is determined by the proper motion of the pulsar. This substructure may be produced by lens-like features in the ionized interstellar medium that are far out of pressure balance with the warm ionized medium and that may be related to deterministic structures that cause extreme scattering events. Observations with this technique, which...