Determine the in-flight annihilation continuum from positrons in circumstellar media

Determine the detailed broad-continuum gamma-ray signal produced by in-flight positron annihilation during positron slowing in the circumstellar medium, including its prospects as a complementary signature for gamma-ray telescopes.

Background

The paper focuses on the narrow 511 keV line generated after positrons injected by dark-photon decays slow down and annihilate or form positronium. A subset of positrons instead annihilates in flight, producing a broad continuum gamma-ray spectrum rather than the narrow line.

Although this continuum could provide an additional observational signature, the paper does not calculate it and explicitly leaves its detailed study for future work.

References

This continuum may provide a complementary signature for $\gamma$-ray telescopes. In this work, however, we focus on the narrow 511~keV signal and leave a detailed study of the in-flight annihilation continuum to future work.

— Probing Feebly Interacting Particles with 511 keV Line from Circumstellar Medium of Supernovae  (2609.18247 - Cheng et al., 16 Sep 2026) in End Matter, Section “Annihilation in flight and positron survival”