Probing the progenitor of high-$z$ short-duration GRB 201221D and its possible bulk acceleration in prompt emission

TL;DR

This paper investigates the origin of the high-redshift short-duration GRB 201221D, analyzing its spectral properties and host galaxy to suggest a compact star merger origin and evidence of bulk acceleration in its prompt emission.

Contribution

It provides a detailed spectral analysis and multi-wavelength criteria to identify the progenitor of GRB 201221D, proposing a Poynting-flux-dominated jet with possible bulk acceleration during prompt emission.

Findings

Spectral fit with cutoff power-law model indicating soft peak energy.

Most observations favor a compact star merger origin.

Evidence of bulk acceleration in the prompt emission phase.

Abstract

The growing observed evidence shows that the long- and short-duration gamma-ray bursts (GRBs) originate from massive star core-collapse and the merger of compact stars, respectively. GRB 201221D is a short-duration GRB lasting $\sim 0.1$ s without extended emission (EE) at high redshift $z=1.046$. By analyzing data observed with the Swift/BAT and Fermi/GBM, we find that a cutoff power-law model can adequately fit the spectrum with a soft $E_{\rm p}=113^{+9}_{-7}$ keV, and isotropic energy $E_{\gamma,iso} =1.36^{+0.17}_{-0.14}\times 10^{51}~\rm erg$. In order to reveal the possible physical origin of GRB 201221D, we adopted multi-wavelength criteria (e.g., Amati relation, $\varepsilon$-parameter, amplitude parameter, local event rate density, luminosity function, and properties of the host galaxy), and find that most of the observations of GRB 201221D favor a compact star merger origin. Moreover, we find that $\hat{\alpha}$ is larger than $2+\hat{\beta}$ in the prompt emission phase which suggests that the emission region is possibly undergoing acceleration during the prompt emission phase with a Poynting-flux-dominated jet.