SN1957D , located in one of the spiral arms of M83 , is one of the small number of extragalactic supernovae that has remained detectable at radio and optical wavelengths during the decades after its explosion .
Here we report the first detection of SN1957D in X-rays , as part of a 729 ks observation of M83 with Chandra .
The X-ray luminosity ( 0.3 - 8 keV ) is 1.7 ^ { +2.4 } _ { -0.3 } \times 10 ^ { 37 } \ > \ > { ergs\ > s ^ { -1 } } .
The spectrum is hard and highly self-absorbed compared to most sources in M83 and to other young supernova remnants , suggesting that the system is dominated at X-ray wavelengths by an energetic pulsar and its pulsar wind nebula .
The high column density may be due to absorption within the SN ejecta . HST WFC3 images resolve the supernova remnant from the surrounding emission and the local star field .
Photometry of stars around SN1957D , using WFC3 images , indicates an age of less than 10 ^ { 7 } years and a main sequence turnoff mass more than 17 \ > M _ { \sun } .
New spectra obtained with Gemini-South show that the optical spectrum continues to be dominated by broad [ O iii ] emission lines , the signature of fast-moving SN ejecta .
The width of the broad lines has remained about 2700 \ > { km\ > s ^ { -1 } } ( FWHM ) .
The [ O iii ] flux dropped precipitously between 1989 and 1991 , but continued monitoring shows the flux has been almost constant since .
In contrast , radio observations over the period 1990-2011 show a decline rate S _ { \nu } \sim t ^ { -4.0 } , far steeper than the rate observed earlier , suggesting that the primary shock has overrun the edge of a pre-SN wind .

Subject Headings : galaxies : individual ( M83 ) – galaxies : ISM – radio continuum : galaxies – supernova remnants – X-rays : general – X-rays : individual ( SN 1957D , M83 ) – supernovae : individual ( SN 1957D )