Radiatively Inefficient Accretion Flow Models of Sgr A*

Abstract

I review radiatively inefficient accretion flow models for the ≈2.6 × 106 M⊙ black hole (BH) in the Galactic Center. I argue for a ‘concordance model’ of Sgr A*: both theory and observations suggest that hot ambient gas around the BH is accreted at a rate ∼10–8 M⊙ yr–1 much less than the canonical Bondi rate. I interpret Chandra observations of Sgr A* in the context of such a model: (1) the extended ‘quiescent’ X-ray emission is due to thermal bremsstrahlung from gas in the vicinity of the Bondi accretion radius, and (2) the ∼104 second long X-ray flares are due to synchrotron or Inverse-Compton emission by non-thermal electrons accelerated in the inner ∼10 Schwarzschild radii of the accretion flow.