Variability of Sagittarius A* at 3 GHz on minute scales with MeerKAT

The supermassive black hole Sagittarius A* (Sgr A*) exhibits temporal and spectral variability across the electromagnetic spectrum. However, variability at radio frequencies below ∼5 GHz for timescales shorter than a day remains largely unexplored. We investigated the variability of Sgr A* at 2.79 GHz on short timescales (1 min) to probe an under-explored regime of its emission process. Through point-source model fitting in the uv domain, we analysed the flux density variation of Sgr A* over an 8 h observation. We detect flux variation on timescales of a few tens of minutes with a modulation index of 6.11%, a mean flux density of (827 ± 0.1 stat ± 33 sys ) mJy, and a mean spectral slope of 0.08 ± 0.03. Furthermore, we measure the slope of the structure function of the observed light curve to be 0.81 ± 0.05 with a characteristic timescale of about 120 min. Our study at low radio frequencies is a critical step towards constraining the physical mechanisms that drive Sgr A*’s variable emission and its spectral energy distribution. Our study suggests that variability at centimetre and millimetre wavelengths is likely more closely related than previously thought.