We report on the discovery of X-ray emission from SN 1970G in M101 , 35 years after its outburst , using deep X-ray imaging with the Chandra X-ray observatory .
The Chandra ACIS spectrum shows that the emission is soft ( { { { { \mathrel { \mathchoice { \vbox { \offinterlineskip \halign { \cr } $ \displaystyle < $ \cr$% \displaystyle \sim$ } } } { \vbox { \offinterlineskip \halign { \cr } $ \textstyle < $ \cr$% \textstyle \sim$ } } } { \vbox { \offinterlineskip \halign { \cr } $ \scriptstyle < $ \cr$% \scriptstyle \sim$ } } } { \vbox { \offinterlineskip \halign { \cr } $ \scriptscriptstyle < $% \cr$ \scriptscriptstyle \sim$ } } } } 2 keV ) and characteristic for the reverse shock region .
The X-ray luminosity , L _ { 0.3 - 2 } = ( 1.1 \pm 0.2 ) \times 10 ^ { 37 } ~ { } { ergs~ { } s } ^ { -1 } , is likely caused by the interaction of the supernova ( SN ) shock with dense circumstellar matter .
If the material was deposited by the stellar wind from the progenitor , a mass-loss rate of \dot { M } = ( 2.6 \pm 0.4 ) \times 10 ^ { -5 } ~ { } M _ { \odot } ~ { } { 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 \propto t ^ { - s } with index s = 1.7 \pm 0.6 over a period of 12–35 years after the outburst .
As the oldest SN detected in X-rays , SN 1970G allows , for the first time , direct observation of the transition from a SN to its supernova remnant ( SNR ) phase .