Characterization of the production of intense Alfv\'en pulses : GRMHD simulation of black hole accretion disks

The episodic dynamics of the magnetic eruption of a spinning black hole (BH) accretion disks and its associated intense shapeup of their jets is studied via three-dimensional general-relativistic magnetohydrodynamics (GRMHD). The embedded magnetic fields in the disk get amplified by the magnetorotational instability (MRI) so large as to cause an eruption of magnetic field (recconection) and large chunks of matter episodically accrete toward the roots of the jets upon such an event. We also find that the eruption events produce intensive Alfv\'en pulses, which propagate through the jets. After the eruption, the disk backs to the weakly magnetic states. Such disk activities cause short time variabilities in mass accretion rate at the event horizon as well as electric-magnetic luminosity inside the jet. Since the dimensionless strength parameter $a_0=eE/m_e \omega_{\rm A}c$ of these Alfv\'en wave pulses is extremely high $\sim 10^{10}$ for the $10^8$ solar masses central black hole and $10$\% Eddington accretion rate accretion flow, the bow wake acceleration model proposed by Ebisuzaki \& Tajima (2014) certainly works to accelerate the ultra-high energy cosmic rays and electrons which finally emit gamma-rays. Since our GRMHD model has universality in its spatial and temporary scales, it is applicable to a wide range of astrophysical objects ranging from those of AGN (which is the primary target of this research), to micro-quasars, and down to young stellar objects. Properties such as time variabilities of blazar gamma-ray flares and spectrum observed by {\it Fermi} Gamma-ray Observatory are well explained by linear acceleration of electrons by the bow wake.