A DM fit has positive curvature in 80 observed CHIME Catalog 2 days of FRB 20180916B with linear shape terms and independent 60-day blocks
We tested time trends in fitted dispersion measure (DM) in CHIME/FRB Catalog 2. Coverage rules selected FRB 20180916B and FRB 20190303A. We gave each observed day equal weight and used a linear model with peak frequency, bandwidth, and log width. The primary linear slopes were +0.0257 and -0.0347 pc cm^-3 yr^-1. Both 95% intervals included zero. A planned secondary quadratic check gave +0.0532 [0.0163, 0.0901] pc cm^-3 yr^-2 for FRB 20180916B, from 102 bursts on 80 days. A restricted wild cluster test, with independent 60-day blocks, gave p = 0.0021. Holm correction across two linear and two quadratic tests gave p = 0.0084. The combined correction and extra checks were fixed after the first quadratic results. The 95% interval stayed above zero with 30-day and 90-day blocks, a shifted block origin, and single-component events. Huber and block-deletion estimates were positive. The time-only quadratic interval included zero. FRB 20190303A had no resolved quadratic term. Thus, the evidence supports a curved catalog fit under a linear shape model. It does not establish a change in the physical electron column. The package contains code, derived event data, source hashes, selection audits, plans, figures, and reproduction checks.
fast radio bursts · dispersion measure · CHIME Catalog 2 · FRB 20180916B · FRB 20190303A · time trends · wild cluster bootstrap · reproducible analysis
References
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This work uses numerical measurements from CHIME/FRB Catalog 2, release 20251231.
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This work extends the daily shape model to two sources selected by coverage. It adds time-block inference and a planned quadratic check. No code was copied.
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