Exploring Origin of Ultra-Long Gamma-ray Bursts: Lessons from GRB 221009A

TL;DR

This study investigates the origins of the ultra-long gamma-ray burst GRB 221009A by analyzing its properties, comparing it with a sample of similar GRBs, and simulating progenitor star evolution, suggesting collapsars or magnetars as possible engines.

Contribution

It introduces a statistical classification of GRBs based on duration, analyzes GRB 221009A within this framework, and uses stellar evolution simulations to propose potential progenitors.

Findings

GRB 221009A falls into the Gold sub-sample indicating ULGRB characteristics.

The analysis favors a collapsar scenario with a hyper-accreting black hole as the central engine.

Rotating low-metallicity massive stars could be progenitors of ULGRBs according to MESA simulations.

Abstract

The brightest Gamma-ray burst (GRB) ever, GRB 221009A, displays ultra-long GRB (ULGRB) characteristics, with a prompt emission duration exceeding 1000 s. To constrain the origin and central engine of this unique burst, we analyze its prompt and afterglow characteristics and compare them to the established set of similar GRBs. To achieve this, we statistically examine a nearly complete sample of Swift-detected GRBs with measured redshifts. Categorizing the sample to Bronze, Silver, and Gold by fitting a Gaussian function to the log-normal of T$_{90}$ duration distribution and considering three sub-samples respectively to 1, 2, and 3 times of the standard deviation to the mean value. GRB 221009A falls into the Gold sub-sample. Our analysis of prompt emission and afterglow characteristics aims to identify trends between the three burst groups. Notably, the Gold sub-sample (a higher likelihood of being ULGRB candidates) suggests a collapsar scenario with a hyper-accreting black hole as a potential central engine, while a few GRBs (GRB 060218, GRB 091024A, and GRB 100316D) in our Gold sub-sample favor a magnetar. Late-time near-IR (NIR) observations from 3.6m Devasthal Optical Telescope (DOT) rule out the presence of any bright supernova associated with GRB 221009A in the Gold sub-sample. To further constrain the physical properties of ULGRB progenitors, we employ the tool MESA to simulate the evolution of low-metallicity massive stars with different initial rotations. The outcomes suggest that rotating ($\Omega \geq 0.2\,\Omega_{\rm c}$) massive stars could potentially be the progenitors of ULGRBs within the considered parameters and initial inputs to MESA.