  We present a model for gamma-ray bursts where a dissipative photosphere
provides the usual spectral peak around MeV energies accompanied by a
subdominant thermal component. We treat the initial acceleration of the jet in
a general way, allowing for magnetic field- and baryon dominated outflows. In
this model, the GeV emission associated with GRBs observed by Fermi LAT, arises
as the interaction of photospheric radiation and the shocked electrons at the
deceleration radius. Through recently discovered correlations between the
thermal and non-thermal peaks within individual bursts, we are able to infer
whether the jet was Poynting flux or baryon dominated.
