The Cygnus Loop: a weak core-collapse SN in our Galaxy

Context. The Cygnus Loop is thought to be the result of a core-collapse supernova (SN) explosion in the cavity formed by the wind of the progenitor star. Since then the shock has run through the low-density cavity, hit the cavity wall, and it is now running into a denser environment. Aims. We test the consistency of the global parameters of the remnant (as derived at the cavity-cloud interface) with the observational scenario in the north-east (NE) sector of the remnant. Methods. The test is performed with the help of a time-dependent spherically-symmetric hydrodynamical (HD) code using a smooth density distribution at the cavity-cloud interface. Results. When the shock hits the wall of the cavity, the reflected perturbation is found not to be a shock wave but a strong compression wave. The reflected wave heats up the cavity at temperatures higher than those observed in the X-rays. We also find an outwardly decreasing temperature as observed in X-rays, but over a narrower radial interval. After crossing the wall of the cavity, the shock velocity in the cloud is not steady. Nonetheless, we find that the steady-state assumption usually made to fit the line emission of Balmer-dominated non-radiative filaments (NRFs) can be rather accurate (shock velocity variations