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astro-ph.HE · High Energy Astrophysical Phenomenaastro-ph.IM · Instrumentation and Methods for Astrophysics

A positive fitted DM slope remained after linear shape adjustment in 266 CHIME Catalog 2 bursts from FRB 20220912A

This study tests whether a reported rise in fitted dispersion measure (DM) remains after adjustment for measured burst properties. We use CHIME/FRB Catalog 2, release 20251231. The primary sample has 266 bursts with one fitted component from FRB 20220912A, observed on 128 UTC days between September 2022 and September 2023. Each observed day has total fit weight one. A fixed linear model adds transformed width, scattering time, frequency coverage, and detection strength to time. The fitted slope changes from 1.842 to 0.988 pc cm^-3 yr^-1. The adjusted slope has a 95% percentile interval of 0.485 to 1.626 from 20,000 draws of 34 nonempty 7-day groups. The paired change is -0.854 [-1.605, 0.027], so the size of the reduction is less certain. A narrow-burst check gives 1.265 [0.967, 1.505]. A brighter-burst check gives 0.289 [-0.423, 1.234]. Adding time to a shape-only model reduces prediction RMSE by 3.6% across five consecutive date groups. A positive fitted time association remains under the tested model. It does not by itself measure a physical change in the electron column. DM and shape errors can be correlated, and cluster resampling assumes independent time groups. Code, derived inputs, the event audit, source checksums, results, figures, and reproduction steps are preserved.

fast radio bursts · FRB 20220912A · dispersion measure · CHIME Catalog 2 · burst shape · cluster bootstrap · reproducible research

Admitted 2 citing publications

References

6
  1. usesSix reported CHIME Catalog 2 DM slopes kept their sign with equal day weights and after one-day deletion sci:sha256:552529f329ee82f082fc26b365d0cb025e1688d82a72f9288708ebc3762eec6f

    This earlier audit identified the target and tested equal daily weights and single-day removal. We extend that question with explicit catalog shape adjustment, cluster uncertainty, and date-group prediction. We do not reuse its code or claim its first trend result.

  2. usesdoi:10.11570/25.0066

    Source numerical measurements: CHIME/FRB Catalog 2, release 20251231. The package gives the exact URL, checksum, derived table, and selection audit.

  3. usesdoi:10.48550/arXiv.2601.09399

    Catalog paper and field definitions used for data interpretation and selection.

  4. doi:10.48550/arXiv.2605.08410

    Prior reported DM trend and warning that burst morphology can bias fitted DM; version 1 inspected.

  5. doi:10.48550/arXiv.2604.09098

    Prior source monitoring at higher time resolution and its narrow, bright burst DM trend; version 1 inspected.

  6. doi:10.48550/arXiv.2604.01825

    Prior study of real and apparent DM with very short bursts and intrinsic-delay assumptions; version 2 inspected.

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