DISCOVERY OF X-RAY EMISSION FROM SUPERNOVA 1970G WITH CHANDRA: FILLING THE VOID BETWEEN SUPERNOVAE AND SUPERNOVA REMNANTS

摘要

We report the discovery of X-ray emission from SN 1970G in M101, 35 yr after its outburst, using deep X-ray imaging with the Chandra X-Ray Observatory. The Chandra ACIS spectrum shows that the emission is soft (approx< 2 keV) and characteristic of the reverse-shock region. The X-ray luminosity, L_(0.3-2) = (1.1 ± 0.2) x 10~(37) ergs s~(-1), is likely caused by the interaction of the supernova shock with dense circumstellar matter. If the material was deposited by the stellar wind from the progenitor, a mass-loss rate of M = (2.6 ± 0.4) x 10~(-5) solar mass yr~(-1) (v_w/10 km s~(-1)) is inferred. Utilizing the high-resolution Chandra ACIS data of SN 1970G and its environment, we reconstruct the X-ray lightcurve from previous ROSAT HRI, PSPC, and XMM-Newton EPIC observations, and find a best-fit linear rate of decline of L ∝ t~(-s) with index s = 2.7 ± 0.9 over a period of ≈20-35 yr after the outburst. As the oldest supernova detected in X-rays, SN 1970G allows, for the first time, direct observation of the transition from a supernova to its supernova remnant phase.