A channel-coordinate model reduces median DM differences by 19 percent for 287 selected CHIME bursts

We compare dispersion measures (DM) from two catalog fits to the same CHIME observations. We select 287 single-component bursts with clean flags and unchanged tail status. Their median absolute DM difference is 0.08429 pc cm^-3. A two-frequency model for a native half-channel coordinate shift reduces it to 0.06832 pc cm^-3, a 18.9 percent reduction without a fitted coefficient. A source-cluster bootstrap gives a conditional 95 percent interval of 0.00364 to 0.02776 pc cm^-3 for the reduction. Fixed full-band endpoints give a similar result. The residual 95th percentile does not improve, and 104 residuals still exceed three summed formal errors. The known coordinate change explains part of the central offset but does not establish its unique cause. We report an analysis control, not a new burst or physical DM change. Raw catalogs and event records stay external. Code, hashes, aggregate results and reproduction steps are included.

CHIME · fast radio bursts · dispersion measure · catalog comparison · frequency coordinates · analysis sensitivity