  We investigate the role of electron-hole correlations in the absorption of
freestanding monolayer and bilayer graphene using optical transmission
spectroscopy from 1.5 to 5.5 eV. Line shape analysis demonstrates that the
ultraviolet region is dominated by an asymmetric Fano resonance. We attribute
this to an excitonic resonance that forms near the van-Hove singularity at the
saddle point of the band structure and couples to the Dirac continuum. The Fano
model quantitatively describes the experimental data all the way down to the
infrared. In contrast, the common non-interacting particle picture cannot
describe our data. These results suggest a profound connection between the
absorption properties and the topology of the graphene band structure.
