  Electrons in moir\'e flat band systems can spontaneously break time reversal
symmetry, giving rise to a quantized anomalous Hall effect. Here we use a
superconducting quantum interference device to image stray magnetic fields in
one such system composed of twisted bilayer graphene aligned to hexagonal boron
nitride. We find a magnetization of several Bohr magnetons per charge carrier,
demonstrating that the magnetism is primarily orbital in nature. Our
measurements reveal a large change in the magnetization as the chemical
potential is swept across the quantum anomalous Hall gap consistent with the
expected contribution of chiral edge states to the magnetization of an orbital
Chern insulator. Mapping the spatial evolution of field-driven magnetic
reversal, we find a series of reproducible micron scale domains whose
boundaries host chiral edge states.
