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The supermassive black hole in the center of the Milky Way, Sgr A*, displaysa nearly flat radio spectrum that is typical for jets in active galacticnuclei. Indeed, time-dependent magnetized models of radiatively inefficientaccretion flows (RIAFs), which are commonly used to explain the millimeter,near-infrared, and X-ray emission of Sgr A*, often also produce jet-likeoutflows. However, the emission from these models has so far failed toreproduce the flat radio spectrum. Aims: We investigate whether currentaccretion simulations can produce the compact flat spectrum emission by simplyusing a different prescription for the heating of the radiating particles inthe jet. Methods: We studied the radiative properties of accretion flows onto ablack hole produced in time-dependent general-relativistic magnetohydrodynamic(GRMHD) simulations. A crucial free parameter in these models has always beenthe electron temperature, and here we allowed for variations in theproton-to-electron temperature ratios in the jet and disk. Results: We foundthat the flat spectrum is readily reproduced by a standard GRMHD model if onehas an almost isothermal jet coupled to a two-temperature accretion flow. Thelow-frequency radio mission comes from the outflowing sheath of mattersurrounding the strongly magnetized nearly empty jet. The model is consistentwith the radio sizes and spectrum of Sgr A*. Conclusions: Hence, GRMHD modelsof accreting black holes can in principle naturally reproduce jets that matchobserved characteristics. For Sgr A* the model fit to the spectrum predictshigher mass-accretion rates when a jet is included than without a jet. Hence,the impact of the recently discovered G2 cloud that is expected to be accretedonto Sgr A* might be less severe than currently thought.

Coupled jet-disk model for Sgr A*: explaining the flat-spectrum radio core with GRMHD simulations of jets