GRB 201104A: A "Repetitive" Short Gamma-Ray Burst?

TL;DR

This paper investigates a peculiar gamma-ray burst, GRB 201104A, which exhibits repetitive behavior typically associated with short bursts, challenging the traditional classification and exploring possible lensing effects through Bayesian analysis.

Contribution

The study identifies and analyzes a long-duration GRB with short-burst characteristics and repetitive behavior, proposing lensing as a potential explanation and extending spectral analysis with Bayesian inference.

Findings

GRB 201104A shows repetitive behavior with similar spectra in different periods.

No strong evidence supports gravitational lensing as the cause.

The event challenges the current GRB classification scheme.

Abstract

Gamma-ray bursts (GRBs) are divided into short gamma-ray bursts (SGRBs) and long gamma-ray bursts (LGRBs) based on the bimodal distribution of their durations. LGRBs and SGRBs are typically characterized by different statistical characteristics. Nevertheless, there are some samples that challenge such a framework, such as GRB 060614, a long-duration burst with short-burst characteristics. Furthermore, GRBs are generally considered to be an event with no periodic or repetitive behavior, since the progenitors usually undergo destructive events, such as massive explosions or binary compact star mergers. In this work, we investigated Fermi data for possible quasiperiodic oscillations and repetitive behaviors of GRBs using timing analysis methods and report a special event GRB 201104A, which is a long-duration burst with the characteristics of an SGRB, and it exhibits a "repetitive" behavior. We propose that such a situation may arise from lensed SGRBs and attempt to verify it by Bayesian inference. In addition, we extend the spectral analysis to Bayesian inference. In spite of the existence of at least two distinct time periods with a nearly identical spectrum, there is no strong evidence that they result from a lensing GRB. Taking the gravitational-lensing scenario out of consideration, a long burst would resemble a short burst in its repetitive behavior, which presents a challenge for the current classification scheme.