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It has been suggested that the prompt emission in gamma-ray bursts (GRBs)could be described by radiation from the photosphere in a hot fireball. Suchmodels must be tested by directly fitting them to data. In this work we usedata from the Fermi Gamma-ray Space Telescope and consider a specificphotospheric model, in which kinetic energy of a low-magnetisation outflow isdissipated locally by internal shocks below the photosphere. We construct atable model with a physically motivated parameter space and fit it totime-resolved spectra of the 36 brightest Fermi GRBs with known redshift. Wefind that about two thirds of the examined spectra cannot be described by themodel, as it typically under-predicts the observed flux. However, since thesample is strongly biased towards bright GRBs, we argue that this fraction willbe significantly lowered when considering the full population. From thesuccessful fits we find that the model can reproduce the full range of spectralslopes present in the sample. For these cases we also find that the dissipationconsistently occurs at a radius of $\sim 10^{12}$ cm and that only a fewpercent efficiency is required. Furthermore, we find a positive correlationbetween the fireball luminosity and the Lorentz factor. Such a correlation hasbeen previously reported by independent methods. We conclude that if GRBspectra are due to photospheric emission, the dissipation cannot only be thespecific scenario we consider here.

Testing a model for subphotospheric dissipation in GRBs: fits to Fermi data constrain the dissipation scenario