Establish the significance of the prompt spectral hardening and the number of distinct ejecta

Establish the statistical significance of the later gamma-ray spectral hardening and determine the number of distinct ejecta responsible for the prompt emission of EP251222b/GRB 251222A.

Background

The time-resolved spectral analysis finds suggestive hardening during the later bright gamma-ray interval, while the shell-collision model interprets separate prompt episodes as evidence for distinct ejecta. The paper explicitly notes that the hardening has not been subjected to a dedicated hypothesis test and that the number of ejecta remains unresolved.

A dedicated model comparison is needed to assess whether the spectral change is statistically significant and whether the prompt light curve requires multiple ejecta components.

References

However, their statistical significance has not been established with a dedicated model comparison. Future events with better pulse sampling may discriminate via spectral-hardness resets and bimodal lag distributions between shell groups.

— A Shell Collision Scenario for EP251222b/GRB 251222A: Connecting Prompt Emission and Double-Peaked Afterglow  (2610.21583 - Shi et al., 15 Oct 2026) in Section 5, Discussion