Sophia Sanchez-Maes, University of Maryland  3D Particle-in-Cell Simulations of Reconnection-Driven Particle Acceleration and Their Implications for Sagittarius A Flares  The brightest X-ray flares from Sagittarius A* (Sgr A*) reveal extreme episodes of particle acceleration. Explaining observed spectra requires electrons accelerated to Lorentz factors in the range of hundreds of thousands to millions, which is beyond what traditional approaches have demonstrated in this context. Magnetic reconnection offers a compelling mechanism, capable of efficiently accelerating particles to high energies. However, two-dimensional (2D) particle-in-cell (PIC) simulations have intrinsic limitations: particle motion is confined within plasmoids, restricting energy gain. Acceleration in 2D reconnection typically saturates near the plasma magnetization limit, falling short of the energies required to explain the brightest X-ray flares. In contrast, 3D reconnection introduces additional degrees of freedom, allowing particles to escape plasmoids and enhancing acceleration efficiency.
To connect reconnection physics with observed Sgr A* flare spectra, weperform 3D PIC simulations spanning a range of magnetic guide fieldstrengths (Bg/B0), and investigate the resulting particle accelerationand synchrotron spectra. We find that the guide field plays animportant role: a strong guide field limits particle energies andsoftens the spectrum, while a weak or absent guide field in 3Dproduces overly hard power-law slopes. Intermediate guide fieldstrengths yield particle distributions more consistent with thoseobserved during X-ray flares from Sgr A*. These initial resultssuggest that reconnection-mediated acceleration can plausibly powerthe IR and X-ray variability observed near the Galactic Center'ssupermassive black hole. The strength of the guide magnetic field mayfurther regulate whether flare emission extends into the X-ray,consistent with the fact that all Sgr A* X-ray flares have IRcounterparts, but not all IR flares produce observed X-rays.