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Many different physical processes have been suggested to explain the promptgamma-ray emission in gamma-ray bursts (GRBs). Although there are examples ofboth bursts with photospheric and synchrotron emission origins, these distinctspectral appearances have not been generalized to large samples of GRBs. Here,we search for signatures of the different emission mechanisms in the full FermiGamma-ray Space Telescope GBM catalogue. We use Gaussian Mixture Models tocluster bursts according to their parameters from the Band function ($\alpha$,$\beta$, and $E_{pk}$) as well as their fluence and $T_{90}$. We find fivedistinct clusters. We further argue that these clusters can be divided intobursts of photospheric origin (2/3 of all bursts, divided into 3 clusters) andbursts of synchrotron origin (1/3 of all bursts, divided into 2 clusters). Forinstance, the cluster that contains predominantly short bursts is consistent ofphotospheric emission origin. We discuss several reasons that can determinewhich cluster a burst belongs to: jet dissipation pattern and/or the jetcontent, or viewing angle.

Clustering of gamma-ray burst types in the Fermi-GBM catalogue: indications of photosphere and synchrotron emissions during the prompt phase