Hydrodynamical models for X-ray emissions from SN 1993J in M81

X-ray emissions from SN 1993J have been observed from its early stages. To identify the X-ray emission mechanism and constrain the still unknown model parameters for SN 1993J, we have carried out hydrodynamical calculations of the collision between the supernova ejecta and the circumstellar matter for the parameterized ejecta models. We have found that the observed features of X-rays can be accounted for with thermal bremsstrahlung emission from the shock-heated ejecta. To reproduce the observed hardness of the X-ray emission, however, expansion velocities of the ejecta must be fairly high, and the density gradient of the ejecta must be relatively shallow. This is consistent with a relatively low mass envelope of the progenitor, i.e., the Type IIb supernova model.