Accretion onto nearby supermassive black holes: Chandra constraints on thedominant cluster galaxy NGC 6166

Chandra observations of low-luminosity supermassive black holes in nearby e lliptical galaxies provide tight limits on both their nuclear luminosities and their Bondi accretion rates. We examine Chandra constraints on NGC 6166 , the dominant galaxy in the cluster Abell 2199, which hosts an similar to 10(9) M-., black hole. We measure a nuclear X-ray luminosity of L-X,L- 1 ke V similar to 10(40) ergs s(-1) and show that the density and temperature pr ofiles of the hot interstellar medium imply a Bondi accretion rate of (M) o ver dot(Bondi) less than or similar to 3 x 10(-2) M-. yr(-1). This accretio n rate predicts a nuclear luminosity of similar to 10(44) ergs s(-1) for a canonical radiative efficiency of 10%. Unless the Bondi estimate is inappro priate and/or the accretion rate onto the black hole is significantly reduc ed, the observed nuclear flux constrains the radiative efficiency of the ac cretion flow to be eta similar to 10(-5). We show that low radiative effici ency accretion flows can explain the observed nuclear X-ray luminosity but that the power output from the jets in NGC 6166 is also important to the en ergetics of the system.