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Abstract
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 rely on a large flux density and/or a large collecting area, have an angular resolution of about a milliarcsecond. They often show features in the scatter broadened image out to 15–20 times this resolution. Thus, single-dish observations can study details in the scattering medium on AU-size scales while covering a relatively large field of view that scans the sky at the pulsar proper motion speed. We are still learning how to interpret the richly detailed scintillation arc pattern that results, and observational and interpretive surprises continue to emerge.
Acknowledgements
I thank the organizers of this conference for the opportunity to discuss scintillation in such a congenial setting. This research was supported by grant no. AST-0407302 from the US National Science Foundation.