X-ray Observation of Radio Supernova Sn1979c by Asca

We report on the X-ray observation of the radio selected supernova SN1979C carried out with ASCA in December 1997. The supernova of type IIL was first observed in the optical and occurred in the weakly barred, almost face on spiral galaxy NGC 4321 (M100) which is at a distance of 17.1 Mpc, and contains at least three other supernovae discovered in this century. No point source was detected at the radio position of SN1979C in a 3’ diameter half power response circle in a 27.3 ks SIS exposure. The background and galaxy subtracted SN signal had a 3σ upper limit to the count rate of 1.2×10 cps in the full ASCA SIS band (0.4-10.0 keV). These measurements give the first ever x-ray flux limit of a Type IIL SN in the higher energy band (≥ 2 keV) which is an important diagnostic of the outgoing shock wave ploughing through the circumstellar medium. I X-RAY AND RADIO EMISSION FROM