Letter to the Editor

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

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121, Bonn, Germany
² Argelander Institute for Astronomy, University of Bonn, Auf dem Hügel 71, 53121, Bonn, Germany
³ Deutsches Zentrum für Astrophysik, Postplatz 1, 02826, Görlitz, Germany
⁴ Thüringer Landessternwarte, Sternwarte 5, 07778, Tautenburg, Germany
⁵ Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la Astronomía s/n, E-18008, Granada, Spain
⁶ Center for Astrophysics | Harvard & Smithsonian, Cambridge, MA, 02138-1516, USA
⁷ South African Radio Astronomy Observatory, Liesbeek House, River Park, Cape Town, 7705, South Africa
⁸ Max-Planck-Institut für Gravitationsphysik (Albert Einstein Institute), 30167, Hannover, Germany
⁹ Leibniz Universität Hannover, 30167, Hannover, Germany
¹⁰ SKA Observatory, Jodrell Bank, Lower Withington, Macclesfield, SK11 9FT, United Kingdom

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 6 March 2026
Accepted: 24 April 2026

Abstract

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.