Variability of the Spectrum of the Young Supernova Remnant G11.2-0.3

The spectrum of G11.2-0.3 has been refined by bringing the published intensity measurements to the “artificial moon” flux scale, and the dynamics of its changes on different time scales from 0.4 to more than ~50 years has been investigated. An increase in the fluxes of radio emission of G11.2-0.3 for ≥30 years at 3 cm $$ \leqslant \lambda \leqslant 375$$ cm with a frequency dependence was found: the average rate of changes decreases proportionally to $$\log(f)$$, and at frequencies $$f \geqslant 10$$ GHz, the increase gave way to a decrease. Measurements with the RT-32 radio telescope of the Svetloe observatory (IAA RAS) in 2013–2019 showed a decrease in fluxes of G11.2-0.3 against the background of rapid nonstationary changes with an average rate of ($$ - 5.4 \pm 6.6$$) %/year at a wavelength $$\lambda = 6.2$$cm and ($$ - 1.5 \pm 0.9)$$ %/year at $$\lambda = 3.5$$ cm. The stages of growth and decline of fluxes are separated by an epoch $$2016.9 \pm 0.6$$. The spectrum of G11.2-0.3 is the spectra sum of the shell and the plerion, with each of its parameters determined by the method developed for the 1972.5 epoch. The values of the spectral indices α1 of the shell and α2 of PWN are obtained: $$\alpha {{1}_{{1972}}} = 0.77$$ and $$\alpha {{2}_{{1972}}} = 0.251$$. The dynamics of radio emission from the remnant reflects the scenario of interaction between the shock wave and CSM. Possible reasons for evolutionary and non-stationary changes are discussed.