The Cygnus Loop: A Low-Density Blast Wave Whose Energy Budget Disfavours a Hypernova Reading

This paper computes the energy, density and acceleration budgets of the Cygnus Loop from a small set of adopted, published input values, using the relations stated in the Methods and a deposited script that reproduces every number. The Sedov energy is 1.28 in units of 10^51 erg, a factor 1.28 of the canonical value: at the adopted low mean density, a perfectly ordinary explosion explains the Loop's size, and no exceptional progenitor energy is required. The shock speed of 521 km/s corresponds to a post-shock temperature of 0.325 keV for the diffuse component, while the optical filaments arise in denser gas where the shock is slower and already radiative, a two-phase picture the single-zone numbers frame but cannot reproduce in detail. The calculation is a computation from stated assumptions, not a measurement, and each headline result is reported together with the diagnostic that tests whether the assumed evolutionary phase applies to this object.