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Caption: Figure 10.
Diffractive scattering kernel and refractive noise rms at 1.3 mm based on the scattering model of Psaltis et al. (2018) and Johnson et al. (2018). (a) The image-domain representation of the kernel, with a second moment of 23.6 × 12.1 μas in FWHM at PA = 82°. (b) The normalized kernel amplitude and refractive noise level at 1.3 mm as a function of the baseline length (lines), overlaid on normalized Sgr A* low-band data from 2017 April 7 (circles). The red and blue solid lines show the amplitudes of the kernel along the major and minor axes, respectively. The dashed lines show the rms refractive noise levels for a reference model in Paper III along each axis colored in the same way. The shaded area around each line covers the range of possible amplitude values given the uncertainties of scattering parameters in the model. The Sgr A* amplitudes exhibit a steeper fall-off than that of the scatter-broadening kernel, indicative of resolved dominant intrinsic structure larger than the scattering kernel size. Furthermore, most of the amplitudes are well above the expected range of the refractive noise, implying that the refractive substructure is likely not dominant in the observed structure. The most affected baselines are Chile to Hawai‘i and Spain, Mexico to Spain and the South Pole, and Hawai‘i to the South Pole in the 6 – 8 Gλ range.
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