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

TL;DR

This study investigates minute-scale radio variability of Sagittarius A* at 2.79 GHz using MeerKAT, revealing flux fluctuations and structure function characteristics that inform the understanding of its emission mechanisms.

Contribution

First detailed analysis of short-timescale radio variability of Sgr A* at low frequencies, providing new insights into its emission processes.

Findings

Detected flux variation on tens of minutes with a 6.11% modulation index.

Measured a mean flux density of 827 mJy with low statistical and systematic uncertainties.

Found a structure function slope of 0.81 with a characteristic timescale of about 120 minutes.

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 investigate 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 analyse the flux density variation of Sgr A* over an 8 h observation. We detect flux variation on a few tens of minute timescale with a modulation index of 6.11 %, a mean flux density of ($827 \pm 0.1_{\mathrm{stat}} \pm 33_{\mathrm{sys}}) \, \mathrm{mJy}$, and a mean spectral slope of $0.08\pm0.03$. Furthermore, we measure the slope of the structure function of the observed light curve as $0.81 \pm 0.05$ with a characteristic timescale of about 120 min. Our study at low radio frequencies is a critical step toward 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.