Distinguish the circumburst density profile

Determine whether EP251222b/GRB 251222A propagated through a homogeneous circumburst medium, a wind-like medium, or a density-structured environment.

Background

The afterglow fit assumes a homogeneous external medium shared by the core and wing components. Nevertheless, a wind-like or density-structured environment could also produce the observed optical rebrightening and afterglow behavior. The current observations therefore do not uniquely identify the density profile, leaving the environmental interpretation unresolved.

Additional late-time and continuous multi-band observations would be needed to distinguish environmental structure from dynamical effects associated with the proposed shell collision.

References

While we did not observe any X-ray features in afterglow and the rebrightening in the optical band can be produced by several mechanisms, the present data do not uniquely distinguish a homogeneous medium from a wind-like or density-structured environment.

— 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 4, Results