Identify the source of the systematic excess in recovered host magnitudes

Identify the source of the statistically significant excess of recovered fast radio burst host galaxies with magnitudes between 18 and 21 in the 30-arcsecond localisation-uncertainty synthetic sample.

Background

The combined radio–optical framework reproduces the underlying host-galaxy magnitude distribution substantially better than a traditional PATH-only analysis when the simulated localisation uncertainty is 30 arcseconds. Nevertheless, the recovered distribution contains a slight excess of hosts with 18 < m_r < 21.

The paper reports that this difference is expected to be statistically significant and is not explained by the applied correction to the background-galaxy density. The authors leave unresolved whether the source lies in the radio-population or optical-host framework, motivating a dedicated systematic investigation.

References

We expect that this difference is statistically significant, and may arise from within either the \ or framework. It is not due to the correction factor to the background galaxy density $\rho(m_r)$ of Eq.~\ref{eq:rho_correction}, which produces only a small change in the distribution. We leave studying this systematic to a future analysis, perhaps similar to the methods of B.C., to uncover this error.

— Through a glass, darkly: a combined framework for estimating fast radio burst host galaxy and population properties in an era of uncertain host identification  (2609.04765 - James et al., 4 Sep 2026) in Section 5.4, “Verification of posterior distributions”