Temporal and Spectral Analysis of the Unique and Second Brightest Gamma-Ray Burst GRB 230307A: Insights from GECAM and Fermi/GBM Observations

TL;DR

This paper analyzes the temporal and spectral properties of the exceptionally bright gamma-ray burst GRB 230307A using GECAM and Fermi/GBM data, revealing a transition in emission mechanisms and highlighting the need for more complex models.

Contribution

It provides a joint temporal and spectral analysis of GRB 230307A, including a transition in emission behavior and evaluation of the large-radius internal shock model.

Findings

Initial 27 seconds show consistent synchrotron radiation patterns.

Transition to high latitude emission influenced by shell geometry.

Limitations identified in the large-radius internal shock model.

Abstract

In this study, we present the pulse profile of the unique and the second brightest gamma-ray burst GRB 230307A, and analyze its temporal behavior using a joint GECAM--Fermi/GBM time-resolved spectral analysis. The utilization of GECAM data is advantageous as it successfully captured significant data during the pile-up period of the Fermi/GBM. We investigate the evolution of its flux, photon fluence, photon flux, peak energy, and the corresponding hardness-intensity and hardness-flux correlations. The findings within the first 27 seconds exhibit consistent patterns reported previously, providing valuable insights for comparing observations with predictions from the synchrotron radiation model invoking an expanding shell. Beyond the initial 27 seconds, we observe a notable transition in the emitted radiation, attributed to high latitude emission (HLE), influenced by the geometric properties of the shells and the relativistic Doppler effects. By modeling the data within the framework of the large-radius internal shock model, we discuss the required parameters as well as the limitations of the model. We conclude that a more complicated synchrotron emission model is needed to fully describe the observational data of GRB 230307A.