Proton Cyclotron Features and Multipole Fields: Line-Inferred Strengths Against Spin-Down Dipole Values

A handful of magnetar spectra carry absorption features that, read as proton cyclotron resonances, measure the magnetic field where the photons were absorbed rather than the field inferred from braking at the light cylinder. The two measurements need not agree, and where they disagree the difference maps the multipolar structure close to the surface. Working from published values for the sources concerned, this paper computes the relevant quantities under one stated set of conventions and compares them source by source. Headline results: largest multipole ratio source SGR 0418+5729; largest multipole ratio 65.1; smallest multipole ratio 0.51; line field SGR0418 G 3.97e+14. The comparisons are budget statements: they establish whether the energies, stresses, powers and timescales involved are mutually consistent, and by what margin. Every number quoted is produced by the deposited compute.py script from the stated inputs, and the full per-source record is deposited as results.json alongside the text.