An Unambiguous Separation of Gamma-Ray Bursts into Two Classes from Prompt Emission Alone

Abstract

The duration of a gamma-ray burst (GRB) is a key indicator of its physics origin, with long bursts perhaps associated with the collapse of massive stars and short bursts with mergers of neutron stars.However, there is substantial overlap in the properties of both short and long GRBs and neither duration nor any other parameter so far considered completely separates the two groups. Here we unambiguously classify every GRB using a machine-learning, dimensionality-reduction algorithm, t-distributed stochastic neighborhood embedding (t-SNE), providing a catalog separating all Swift GRBs into two groups. Although the classification takes place only using prompt emission light curves,every burst with an associated supernova is found in the longer group and bursts with kilonovae in the short, suggesting along with the duration distributions that these two groups are truly long and short GRBs. Two bursts with a clear absence of a supernova belong to the longer class, indicating that these might have been direct-collapse black holes, a proposed phenomenon that may occur in the deaths of more massive stars.

Accepted to Astrophysical Journal Letters, 8 pages, 4 figures

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• GRB 201015A and the nature of low-luminosity soft gamma-ray bursts
• Graph-based clustering of gamma-ray bursts
• The interstellar medium in the environment of the supernova-less long-duration GRB 111005A
• Distribution of gamma-ray bursts on the t90-hardness ratio plane and their classification revisited
• Identifying and Repairing Catastrophic Errors in Galaxy Properties Using Dimensionality Reduction