Dipole Magnetic Fields of Eighteen Magnetars from Spin-Down: A Catalogue-Wide Recalculation Against the Quantum Critical Field

The dipole field inferred from a period and a period derivative is the most quoted number in magnetar astronomy and the least often recomputed in one place with one convention. Different papers adopt different inclination factors, different moments of inertia and different rounding, so values for the same source can differ by factors of a few between publications without any new data being involved. 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: highest B source SGR 1806-20; highest B G 1.95e+15; lowest B source SGR 0418+5729; lowest B G 6.10e+12; median B G 2.22e+14; span in B 319.1; sources above BQ 16; n sources 18. 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.