Constraint on the black hole spin of M87 from the accretion-jet model

Abstract

Abstract The millimetre bump, as found in high-resolution multiwaveband observations of M87 by Prieto et al., most possibly comes from the synchrotron emission of thermal electrons in advection-dominated accretion flow (ADAF). It is possible to constrain the accretion rate near the horizon if both the nuclear millimetre emission and its polarization are produced by the hot plasma in the accretion flow. The jet power of M87 has been extensively explored, which is around $8_{\rm -3}^{+7}\times 10^{42}$ erg s−1 based on the analysis of the X-ray cavity. The black hole (BH) spin can be estimated if the jet power and the accretion rate near the horizon are known. We model the multiwavelength spectral energy distribution (SED) of M87 with a coupled ADAF–jet model surrounding a Kerr BH, where the full set of relativistic hydrodynamical equations of the ADAF are solved. The hybrid jet formation model, as a variant of the Blandford–Znajek model, is used to model the jet power. We find that the SMBH should be fast rotating with a dimensionless spin parameter $a_{*}\simeq 0.98_{\rm -0.02}^{+0.012}$.