We present results from observations of SN 1979C with XMM-Newton in X-rays and in the UV , archival X-ray and HST data , and follow-up ground-based optical imaging .
The XMM-Newton MOS spectrum shows best-fit two-temperature thermal plasma emission characteristics of both the forward ( kT _ { high } = 4.1 ^ { +76 } _ { -2.3 } keV ) and reverse shock ( kT _ { low } = 0.78 ^ { +0.25 } _ { -0.17 } keV ) with no intrinsic absorption .
The long-term X-ray lightcurve , constructed from all X-ray data available , reveals that SN 1979C is still radiating at a flux level similar to that detected by ROSAT in 1995 , showing no sign of a decline over the last six years , some 16–23 yrs after its outburst .
The high inferred X-ray luminosity ( L _ { 0.3 - 2 } = 8 \times 10 ^ { 38 } ~ { } { ergs~ { } s } ^ { -1 } ) is caused by the interaction of the SN shock with dense circumstellar matter , likely deposited by a strong stellar wind from the progenitor with a high mass-loss rate of \dot { M } \approx 1.5 \times 10 ^ { -4 } ~ { } M _ { \odot } ~ { } { yr } ^ { -1 } ~ { } ( v _ { w } / 10 ~ { % } { km~ { } s } ^ { -1 } ) .
The X-ray data support a strongly decelerated shock , and show a mass-loss rate history which is consistent with a constant progenitor mass-loss rate and wind velocity over the past { { { { \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$ } } } } 16 , 000 yrs in the stellar evolution of the progenitor .
We find a best-fit CSM density profile of \rho _ { CSM } \propto r ^ { - s } with index { { { { s \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$ } } } } 1.7 and high CSM densities ( { { { { \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$ } } } } 10 ^ { 4 } ~ { } { cm } ^ { -3 } ) out to large radii from the site of the explosion ( { { { { r \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$ } } } } 4 \times 10 ^ { 17 } ~ { } { cm } ) .
Using XMM-Newton Optical Monitor data we further detect a point-like optical/UV source consistent with the position of SN 1979C , with B,U , and UVW 1 -band luminosities of 5 , 7 , and 9 \times 10 ^ { 36 } ~ { } { ergs~ { } s } ^ { -1 } , respectively .
The young stellar cluster in the vicinity of the SN , as imaged by the HST and follow-up ground-based optical imaging , can only provide a fraction of the total observed flux , so that a significant contribution to the output likely arises from the strong interaction of SN 1979C with dense CSM .