Speaker
Description
The EHT observations have highlighted the major role played by large scale magnetic fields around accreting supermassive black holes (BHs), in agreement with the polarimetric results from their stellar-mass siblings. The magnetic field not only funnels an electromagnetic jet but it also accelerate particles when it reconnects and it sometimes even regulates the accretion. The GRAVITY collaboration followed during a NIR flare a centroid shift consistent with a synchrotron-emitting hot spot on a face-on orbit around Sgr A*. Several aspects challenge our understanding though: its super-Keplerian speed, a non-zero velocity along the line-of-sight, the incompleteness of the orbit and a shift of almost 10 gravitational radii between the alleged orbit center and the center of mass deduced from the S2 orbit.
In this talk, I will present 3D global GR-PIC simulations of particle acceleration in the magnetosphere of a spinning BH. I will show that magnetic loops advected into the BH ergosphere are prone to open and feed a current sheet in the sheath of the jet. In this highly magnetized region, magnetic field lines reconnect in the relativistic regime and leptons are accelerated up to Lorentz factors of a few 100 to a few 1,000. At the Y-ring at the basis of the jet’s sheath, a few gravitational radii above the disk, plasmoids form and co-rotate with the footpoint of the outermost closed magnetic field line, hence the apparent super-Keplerian motion. They later detach due to the tearing instability and further propagate along a coiled trajectory on the sheath of the jet. We compute the evolution of the synchrotron emission from these plasmoids and compare it to typical Sgr A* flares.
