Magnetars Against the Quantum Critical Field: A Census of Supercritical and Subcritical Dipole Strengths

At 4.414e13 gauss the magnetic field becomes strong enough that quantum electrodynamic processes with no low-field analogue switch on: photon splitting, vacuum birefringence and single-photon pair creation reshape how radiation escapes. Sorting the magnetar catalogue by field strength in units of this critical value shows which sources live in the supercritical regime and which only appear to. 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 over BQ source SGR 1806-20; highest B over BQ 44.1; sources above BQ 16; sources below BQ 2; median B over BQ 5.02. 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.