Measurement of Spectral Breaks in Pulsar Wind Nebulae with Millimeter-Wave Interferometry

We have observed pulsar wind nebulae (PWNe) in the three supernova remnants G11.2-0.3, G16.7+0.1, and G29.7-0.3 at 89 GHz with the Berkeley-Illinois-Maryland Association array, measuring total flux densities of two of them for comparison with archival data at other frequencies. In G16.7+0.1, we find a break in the spectrum of the PWN at ~26 GHz. In G29.7-0.3, our data suggest a break in the integrated spectrum of the central nebula at ~55 GHz, lower than previously estimated. However, we have found spatial structure in the spectrum of this nebula. The emission to the north of pulsar J1846-0258 has a broken spectrum with break frequency <~100 GHz, consistent with a conventional pulsar-powered nebula. The emission to the south of the pulsar has a nearly power-law spectrum from radio to X-rays: this component may be unrelated to the PWN, or it may be evidence of asymmetries and/or time evolution in the pulsar's energy output. We present 89 GHz images of each remnant.