A possible time-delayed brightening of the Sgr A∗ accretion flow after the pericenter passage of the G2 cloud

Abstract

A possibility of time-delayed radio brightenings of Sgr A∗ triggered by the pericenter passage of the G2 cloud is studied by carrying out global three-dimensional magnetohydrodynamic simulations, taking into account the radiative cooling of the tidal debris of the G2 cloud. Magnetic fields in the accretion flow are strongly perturbed and reorganized after the passage of G2. We have found that the magnetic energy in the accretion flow increased by a factor of 3-4 in 5-10 yr after the passage of G2 through a dynamo mechanism driven by the magneto-rotational instability. Since this B-field amplification enhances the synchrotron emission from the disk and the outflow, the radio and the infrared luminosity of Sgr A∗ are expected to increase some time, around 2020. The time delay of the radio brightening enables us to determine the rotation axis of the preexisting disk.