Resolving the Bondi Accretion Flow toward the Supermassive Black Hole of
  NGC 3115 with Chandra
  Gas undergoing Bondi accretion onto a supermassive black hole (SMBH) becomes
hotter toward smaller radii. We searched for this signature with a Chandra
observation of the hot gas in NGC 3115, which optical observations show has a
very massive SMBH. Our analysis suggests that we are resolving, for the first
time, the accretion flow within the Bondi radius of an SMBH. We show that the
temperature is rising toward the galaxy center as expected in all accretion
models in which the black hole is gravitationally capturing the ambient gas.
There is no hard central point source that could cause such an apparent rise in
temperature. The data support that the Bondi radius is at about 4 arcsec-5
arcsec (188-235 pc), suggesting an SMBH of 2 x 10^9 M_sun that is consistent
with the upper end of the optical results. The density profile within the Bondi
radius has a power-law index of 1.03^{+0.23}_{-0.21} which is consistent with
gas in transition from the ambient medium and the accretion flow. The accretion
rate at the Bondi radius is determined to be {\dot M}_B = 2.2 x 10^{-2} M_sun
yr^{-1}. Thus, the accretion luminosity with 10% radiative efficiency at the
Bondi radius (10^{44} erg s^{-1}) is about six orders of magnitude higher than
the upper limit of the X-ray luminosity of the nucleus.
