Implications from the Velocity Profile of the M87 Jet: A Possibility of a Slowly Rotating Black Hole Magnetosphere

Motivated by the measured velocity profile of M87 jet using KVN and VERA Array (KaVA) Park et al. indicating that starting position acceleration is farther from central engine than predicted in general relativistic magnetohydrodynamic simulations, we explore how to mitigate apparent discrepancy between simulations KaVA observation. We use a semi-analytic model proposed Tomimatsu Takahashi. consistently solving trans-magnetic field structure but neglecting any dissipation effects. By comparing with observed profile, find can reproduce logarithmic feature fit data when choosing $c/(100r_{g}) \lesssim \Omega_{F} c/(70r_{g})$ where $r_{g}$ gravitational radius. While total specific energy (${\cal E}$) changes terminal bulk Lorentz factor jet, slower angular black hole magnetosphere (funnel region) ($\Omega_{F}$) makes light-cylinder radius ($r_{\rm lc}$) larger it consequently pushes out location point acceleration. Using estimated $\Omega_{F}$ further estimate magnetic strength on event horizon scale assuming Blandford-Znajek (BZ) process action. The corresponding flux threading good agreement magnetically arrested disc (MAD) regime.