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″–5″ ( 188–235 pc ) , suggesting an SMBH of 2 \times 10 ^ { 9 } M _ { \odot } 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 \times 10 ^ { -2 } M _ { \odot } 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 .