Title

A Comparative Study of Long and Short GRBs. II. A Multiwavelength Method to Distinguish Type II (Massive Star) and Type I (Compact Star) GRBs

Document Type

Article

Publication Date

7-14-2020

Publication Title

The Astrophysical Journal

Volume

897

Issue

2

First page number:

1

Last page number:

11

Abstract

Gamma-ray bursts (GRBs) are empirically classified as long-duration GRBs (LGRBs, >2 s) and short-duration GRBs (SGRBs, <2 s). Physically they can be grouped into two distinct progenitor categories: those originating from collapse of massive stars (also known as Type II) and those related to mergers of compact stars (also known as Type I). Even though most LGRBs are Type II and most SGRBs are Type I, the duration criterion is not always reliable to determine the physical category of a certain GRB. Based on our previous comprehensive study of the multiwavelength properties of long and short GRBs, here we utilize the naive Bayes method to physically classify GRBs as Type I and Type II GRBs based on multiwavelength criteria. It results in a 0.5% training error rate and a 1% test error rate. Moreover, there is a gap [−1.2, −0.16] in the distribution of the posterior odds, $\mathrm{log}O(\mathrm{II}:{\rm{I}})$, the Type II to Type I probability ratio. Therefore, we propose to use ${ \mathcal O }=\mathrm{log}O(\mathrm{II}:{\rm{I}})+0.7$ as the parameter to classify GRBs into Type I (<0) or Type II (>0). The only confirmed Type I GRB, GRB 170817A, has log $O(\mathrm{II}:{\rm{I}})=-10$. According to this criterion, the supernova-less long GRBs 060614 and 060505 belong to Type I, and two controversial short GRBs 090426 and 060121 belong to Type II.

Keywords

Gamma-ray bursts

Disciplines

Astrophysics and Astronomy | Physical Sciences and Mathematics

Language

English

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