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Fig. 2

image

Top: flux density measurements of Sgr A*, from images made using only the inner 7 mosaic fields of the 12 m array, and the flux density of Sgr A* from an average of the ACA observations, are both plotted against time. Error bars in the horizontal direction represent the scan duration. Vertical error bars in the upper panel include both the uncertainty on the pointing (~1′′) and the uncertainty on the primary beam response function. The vertical error bar of the ACA data additionally includes a potential 20% absolute flux calibration uncertainty, relative to the 12 m array observations. The horizontal error bars for the continuum data of the 12 m-Array observations are shorter than the symbol size. Bottom: intensity ratio between the XX and the YY intensity maps derived from the continuum and the Ci line observations are plotted against time. Filled black and green symbols show the 12 m array measurements from Sgr A* and Titan, respectively. Errors are negligibly small for the snapshot on field 0, which is centered on Sgr A* (see Fig. 1). The Ci line measurements are averages from high S/N spectral channels (see also Fig. 6). Their vertical error bars are given by ±1 standard deviations of the intensity ratio, which were derived from those high S/N spectral channels.

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