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

## TL;DR

This paper models the accretion flow and jet of M87 to constrain the black hole's spin, finding it to be rapidly rotating with a spin parameter around 0.98, based on multi-wavelength observations and relativistic modeling.

## Contribution

It introduces a coupled ADAF-jet model with relativistic equations to estimate the black hole spin from observational data, which is a novel approach for M87.

## Key findings

- Black hole spin of M87 estimated at approximately 0.98.
- The model successfully reproduces the observed spectral energy distribution.
- The accretion-jet system indicates a rapidly rotating black hole.

## Abstract

The millimeter bump, as found in high-resolution multi-waveband observations of M87, 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 millimeter 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 $8_{\rm -3}^{+7}\times10^{42} {\rm erg/s}$ 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 multi-wavelength 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 Blandford-Znajek model, is used to model the jet power. We find that the SMBH should be fast rotating with a dimensionless spin parameter $a_{*}\simeq0.98_{\rm -0.02}^{+0.012}$.