CCA Colloquium: Lorenzo Sironi

Title: Fast and furious: magnetic reconnection in relativistic jets and black hole corona

Relativistic jets of blazars and magnetized coronae of low-luminosity accretion flows, like Sgr A* at our Galactic Center, routinely display fast and bright flares of high-energy emission. Yet, the “engine” responsible for accelerating the emitting particles to ultra-relativistic energies is still unknown. With fully-kinetic particle-in-cell (PIC) simulations, we argue that magnetic reconnection — a process by which magnetic field lines of opposite polarity annihilate, releasing their energy to the particles — can satisfy all the basic conditions for the emission. In blazar jets, we show that reconnection can naturally explain the puzzling ultra-fast bright flares observed at GeV and TeV energies, whose duration can be even shorter than the light-travel time across the black hole that powers the jet. In low-luminosity accretion flows like Sgr A*, we show that reconnection can power both thermal and non-thermal emission, and we produce physically-grounded synthetic images and spectra to be compared with infrared and X-ray observations and with the upcoming results of the Event Horizon Telescope

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