Top panel: Total intensity light curve of Sgr A* in bins of 1 min (blue dots) and the phase calibrator PKS 1830-3602 (red squares) on 21 March 2024 at 2.79 GHz. The error bars include systematic and 1σ statistical uncertainties. Bottom panel: Spectral index (α) variation of Sgr A* over time, derived from sub-band flux measurements. Error bars reflect statistical uncertainties. The dashed line represents the mean α = 0.08 (full). The pink-shaded region indicates the light curve after 08:13 UTC, which shows a rapid decrease in flux density followed by an increase. The data used here are available at the CDS.