*Article* **Two Dimensional Clustering of** *Swift***/BAT and** *Fermi***/GBM Gamma-ray Bursts**

**Lána Salmon 1,2,\* , Lorraine Hanlon 1,2 and Antonio Martin-Carrillo 1,2**


**\*** Correspondence: lana.salmon@ucdconnect.ie

**Abstract:** Studies of Gamma-ray Burst (GRB) properties, such as duration and spectral hardness, have found evidence for additional classes beyond the short-hard (merger) and long-soft (collapsar) prototypes. Several clustering analyses of the duration-hardness plane identified a third, intermediate duration, class. In this work, Gaussian Mixture Model-based (GMM) clustering is applied to the *Swift*/BAT and *Fermi*/GBM samples of GRBs. The results obtained by the hierarchical combination of Gaussian components (or clusters) based on an entropy criterion are presented. This method counteracts possible overfitting arising from the application of Gaussian models to non-Gaussian underlying data. While the initial GMM clustering of the hardness-duration plane identifies three components (short/intermediate/long) for the *Swift*/BAT and *Fermi*/GBM samples, only two components (short/long) remain once the entropy criterion is applied. The analysis presented here suggests that the intermediate duration class may be the result of overfitting, rather than evidence of a distinct underlying population.

**Keywords:** gamma-ray burst; clustering; statistical analysis
