Noodle model for scintillation arcs

I show that narrow, parallel strips of phase-changing material, or 'noodles,' generically produce parabolic structures in the delay-rate domain. Such structures are observed as 'scintillation arcs' for many pulsars. The model assumes that the strips have widths of a few Fresnel zones or less, and are much longer than they are wide. A Kirchhoff integral gives the field scattered by these strips. Along one strip, the integral leads to a stationary-phase point where the strip is closest to the line of sight. Across the strip, integration leads to a 1D Fourier transform, from screen position to observing frequency or time. In the limit of narrow bandwidth and short integration time, the integral reproduces the observed scintillation arcs and secondary arclets. Cohorts of strips parallel to different axes produce multiple arcs, as are often observed. A single strip canted with respect to the rest produces features off the main arc. In agreement with observations, the model predicts that arc curvature narrows proportionately to observing frequency squared, and that arclets progress along the main arc with observing epoch. Physically, the noodles may correspond to filaments or sheets of over-or under-dense plasma, with a normal perpendicular to the line of sight. The noodles may lie along parallel magnetic field lines that carry density fluctuations, perhaps in reconnection sheets. If so, observations of scintillation arcs would allow visualization of magnetic fields in reconnection regions.