Are gamma-ray bursts optically thick?

To test the hypothesis that optically thick neutron-star models can produce very hard spectra if the energy density of the source is as high as it is in a thermal radiation field at a temperature of about 1 MeV, consideration is given to the fate of a quantity E of pure energy. This quantity is initially confined to a sphere in equilibrium at a temperature greater than 1 MeV and then allowed to expand freely. Given the shortcomings of conventional models, the possibility that burst sources could be optically thick and distant should not be dismissed.