What is the accretion rate in NGC 4258?

Abstract

We estimate the accretion rate (M) over dot onto the black hole in the nucleus of NGC 4258. The result is model dependent. We find that a thin disk that is flat out to greater than or equal to 2 x 10(3) GM/c(2) (M = black hole mass) and that has inclination equal to that of the masing disk must have (M) over dot similar or equal to 0.01 M-. yr(-1) for consistency with near-infrared data. A thin disk that is warped at similar to 10(3) GM/c(2) requires (M) over dot greater than or similar to 1.5 x 10(-4) M-. yr(-1) for consistency with near-infrared data. Reasonable warp models and the near-infrared data are not consistent with (M) over dot as low as the 7 x 10(-5) alpha M-. yr(-1) proposed by Neufeld & Maloney. An advection-dominated flow model combined with the X-ray data implies (M) over dot similar or equal to 0.01 M-. yr(-1). Consistency with a tight 22 GHz upper limit on the flux from the central source requires a transition radius of similar to(10-100)GM/c(2), although the 22 GHz upper limit may be relaxed by appeal to free-free absorption. Physical conditions in the observed VLBI jet features can also be related to conditions in the inner accretion how. We conclude with a list of observations that might further constrain (M) over dot.