The Radio and X-Ray Energy Partition of the SGR 1935+2154 Burst of April 2020: Efficiency Bounds for Magnetar Radio Emission

In April 2020 the Galactic magnetar SGR 1935+2154 emitted a millisecond radio burst bright enough to register in fast radio burst surveys, accompanied by an X-ray burst orders of magnitude more energetic. The pair is the only direct calibration of how a magnetar divides its output between the radio band and the high-energy band, and the ratio constrains every model that links magnetars to cosmological fast radio bursts. 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: radio to xray energy ratio 3.0e-06; xray to radio ratio 3.3e+05; radio efficiency percent if xray traces total 0.0003; fluence scale at 6.6kpc radio erg 3.0e+34; magnetar reservoir multiple of xray burst 7.9e+05. 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.