IC 443: Shock Compression and the Hadronic Budget of a Remnant Striking a Molecular Cloud

This paper computes the energy, density and acceleration budgets of IC 443 from a small set of adopted, published input values, using the relations stated in the Methods and a deposited script that reproduces every number. At a target density of ten particles per cubic centimetre the proton-proton loss time is 7.05e+06 years, far longer than the age, so the cloud has consumed only a small share of the stored protons; what the density buys is luminosity per stored proton, roughly ten times that of a typical shell environment, which is why a modest stored population shines so brightly here. The gamma-ray luminosity then requires a stored proton energy of 1.33e+49 erg, a fraction 0.0133 of the explosion energy, an entirely reasonable inventory for a remnant that accelerated particles while its shock was fast and now spends them against the cloud. 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.