X-RAYS FROM SN 1993J AND STRUCTURES OF EJECTA AND CIRCUMSTELLAR MEDIUM

We construct a hydrodynamical model of interaction between the ejecta of SN 1993J and the circumstellar medium (CSM) to account for the basic features of X-ray emissions from SN 1993J as observed with ROSAT, ASCA, and OSSE for the first 600 days. This model consists of a realistic ejecta model and a clumpy CSM. The collision of the ejecta with the CSM creates a forward shock in the ejecta and a reverse shock in the CSM. The reverse shock radiates to form a cooling dense shell, and X-rays from the reverse shock are mostly absorbed by this shell. Early hard X-rays are well modeled as thermal emissions from the CSM. Later softening can be accounted for with emissions from shocked clumps. To avoid the emergence of excess hard X-rays from the ejecta, the explosion energy should be lower than a certain upper limit. The CSM must also have a spatially variable density gradient and be more clumpy in the outer layers. With the clumpy CSM, the ejecta undergoes weak deceleration, which is consistent with optical and radio observations. The possible origin of such a CSM is suggested in terms of binary evolution of the progenitor. Prediction of a possible future X-ray enhancement is made.