Spins of the supermassive black hole in M87: new constraints from TeV observations

Abstract

The rapid TeV $\gamma -$ray variability detected in the well-known nearby radio galaxy M87 implies an extremely compact emission region (5-10 Schwarzschild radii) near the horizon of the supermassive black hole in the galactic center. TeV photons are affected by dilution due to interaction with the radiation field of the advection-dominated accretion flow (ADAF) around the black hole, and can thus be used to probe the innermost regions around the black hole. We calculate the optical depth of the ADAF radiation field to the TeV photons and find it strongly depends on the spin of the black hole. We find that transparent radii of 10 TeV photons are of $5R_{\mathrm{S}}$ and $13R_{\mathrm{S}}$ for the maximally rotating and non-rotating black holes, respectively. With the observations, the calculated transparent radii strongly suggest the black hole is spinning fast in the galaxy. TeV photons could be used as a powerful diagnostic for estimating black hole spins in galaxies in the future.

arXiv comment4 pages, 4 figures. to appear in ApJL

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• Non-thermal Processes in Black-Hole-Jet Magnetospheres
• Constraint on the black-hole spin of M87 from the accretion-jet model
• An accretion-jet model for M87: interpreting the spectral energy distribution and Faraday rotation measure
• Probing the central black hole in M87 with gamma-rays
• Electron-Positron Cascade in Magnetospheres of Spinning Black Holes
• Unbound geodesics from the ergosphere and the M87 jet profile
• Particle acceleration close to the supermassive black hole horizon: the case of M87
• Black hole spin from wobbling and rotation of the M87 jet and a sign of a magnetically arrested disc
• A general relativistic external Compton-scattering model for TeV emission from M87
• Numerical Modeling of Multi-wavelength Spectra of M87 Core Emission
• Direct time radio variability induced by non-axisymmetric standing accretion shock instability: implications for M87
• Spin of the M87 black hole
• The Lense-Thirring effect at work in M87${}^{\ast }$
• Disk evolution of the M87's nucleus observed in 2008
• The no-hair theorems at work in M87${}^{\ast }$