Pulsar scintillation arcs. 1. Frequency dependence

Dynamic spectra of pulsars often show low-level crisscross patterns as well as isolated interference maxima called scintles. Previously, we have shown that a power spectrum analysis of the dynamic spectrum usually exhibits a parabolic arc with a well-determined curvature. A simple analysis predicts that this curvature should scale with observing frequency as v(-2). We report On multifrequency observations of three pulsars at the Arecibo Observatory that are designed to test this prediction and explore the frequency behavior of the power distribution. We find that the Eire curvature scales as expected over more than a factor of 5 in observing frequency (0.43-2.2 GHz). this allows us to compare arc curvature at different frequencies obtained over a long time span. Furthermore, we find that scintillation arcs are a broadband phenomenon: they are present contemporaneously, and with the same general appearance, over a wide frequency range. At higher frequencies (greater than or similar to1 GHz) the arcs are more sharply defined, substructure is more prominent, and inverted subarcs often appear with vertices along the main parabola.