Spectral energy distribution of the inner accretion flow around Sgr A* - clue for a weak outflow in the innermost region

Sgr A* represents a unique laboratory for the detailed study of accretion processes around a low-luminosity supermassive black hole (SMBH). Recent X-ray observations have allowed for spatially resolved modelling of the emission from the accretion flow around the SMBH, placing tight constraints on the flux and spectral shape of the accretion from the inner region with r < 10³R_g, where R_g ≡ GM_BH/c² is the gravitational radius of the black hole of mass M_BH. We present here the first modelling of the multiband spectral energy distribution (SED) of this inner region to better constrain the physical condition of the innermost accretion flow. Our modelling uses the Markov chain Monte Carlo method to fit the SED, accounting for the limitations on the accretion rate at the outer radius of 10³R_g from the earlier works and the domination of the accretion flow within 30R_g to the sub-mm bump. It is found that the fitting results of the outflow index could be very different. If only the most luminous part of the SED, the sub-mm bump, is considered, the outflow index is about 0, while if low-frequency radio data and X-ray data are also included, the outflow index could be 0.37 or even higher. The great difference of the fitting results indicates that the outflow index should be variable along radius, with a strong outflow in the outer region and a weak outflow in the innermost region. Such a weak outflow agrees with numerical simulations and makes it possible to explain the multiband SED even better.