Identifying Observational Signatures of Flux Eruption Events in Supermassive Black Hole Accretion Flows with Machine Learning

Abstract

Simulated black hole accretion flows with strong magnetic fields often exhibit "flux eruption events" (FEEs), transient and localized expulsions of matter near the event horizon due to magnetic reconnection. It may now be possible to image them with the Event Horizon Telescope (EHT), a global network of millimeter-wave observatories that images black holes. Here we use machine learning as an interpretable inference tool to identify observational signatures of FEEs that could be accessible to the EHT. First, we train a convolutional neural network to learn task-relevant representations of FEEs in uncorrupted simulated images. After using this network to label a larger set of images, we then train interpretable models (random forest and logistic regression) to determine observational signatures. We find that during a FEE, images in the millimeter tend toward more diffuse emission, higher linear polarization, and lower total fluxes, but these signatures are weak for most FEEs compared to the usual time variability of these features. Moreover, the Q-U loop rotation rate decreases during FEEs, contrary to a picture in which FEEs could jointly cause both millimeter Q-U loops and flares. Our random forest trained on observable summary statistics achieves ~80% class-weighted accuracy, suggesting that the CNN learns FEE structure not fully mapped onto these traditional summary statistics. Our results imply that image size and polarization fraction can be used to flag candidate FEEs, but high-resolution, high-dynamic range images will still be important to confirm FEEs and test accretion flows for this phenomenon.