  We report observations of electromagnetic electron holes (EHs). We use
multi-spacecraft analysis to quantify the magnetic field contributions of three
mechanisms: the Lorentz transform, electron drift within the EH, and Cherenkov
emission of whistler waves. The first two mechanisms account for the observed
magnetic fields for slower EHs, while for EHs with speeds approaching half the
electron Alfv\'en speed, whistler waves excited via the Cherenkov mechanism
dominate the perpendicular magnetic field. The excited whistlers are
kinetically damped and typically confined within the EHs.
