Oliver Porth (University of Amsterdam)
Title: Dynamics of black hole accretion. Of flux-tubes, plasmoids and transient phenomena
Abstract: Over the last two decades, general relativistic magnetohydrodynamic simulations (GRMHD) have drawn a robust broad-brush picture of black hole accretion and jet formation in low-luminosity sources. The observations by the Event Horizon Telescope and the GRAVITY interferometer now probe accretion physics with unprecedented detail requiring equally sophisticated dynamical models. I will take this opportunity to review the state-of-the-art in 3D numerical source models and discuss new results obtained with the BlackHoleAccretionCode. To investigate variability and flares, we have analyzed distinct dynamical features like orbiting flux tubes and plasmoid chains that occur in the black hole magnetosphere. Flux tubes escaping from the black hole remain coherent for more than one orbital period and could give rise to flares as currently observed with GRAVITY. The simulations of plasmoids show that trans-relativistic magnetic reconnection is naturally triggered in the accretion flow. Consistent modeling of this process could be key in understanding particle heating and acceleration and I will give an outlook on simulations with the BlackHoleAccretionCode that include plasma resistivity.
Michael Janssen (Radboud University)
Title: Simulating the full VLBI datapath to explore future EHT observations
Abstract: I will present SYMBA, a novel end-to-end VLBI synthetic data generation pipeline. We use a model of a magnetized accretion flow around a black hole in general relativity and compute the expected millimeter emission. The radiation is then propagated through Earth's atmosphere and we simulate the received signal plus noise at every telescope of the array, while taking weather effects into account. Finally, the data from this simulated observation is passed through standard EHT calibration and imaging software such that a source model is reconstructed in the same way as for real data. We are therefore able to predict how the EHT would 'see' a specific model. Using SYMBA, I will demonstrate the effect of different weather conditions on EHT data and how future observations will allow us to measure model parameters more accurately compared to the M87* result from the 2017 observations.