An international team of astronomers has used NASA’s Chandra X-ray Observatory to make the first detection of X-rays from the remains of a supernova that was first seen from Earth over 50 years ago. While detected in the radio and optical for decades, the supernova SN 1957D did not appear in previous X-ray images.
SN 1957D was discovered in 1957 in M83, a spiral galaxy about 15 million light years from Earth. It is one of only a few located outside of the Milky Way galaxy that is detectable, in both radio and optical wavelengths, decades after its explosion was observed. In 1981, astronomers saw the remnant of the exploded star in radio waves, and then in 1987 they detected the remnant at optical wavelengths, years after the light from the explosion itself became undetectable.
A relatively short observation – about 14 hours long – from NASA’s Chandra X-ray Observatory in 2000 and 2001 did not detect any X-rays from the remnant of SN 1957D. However, a much longer observation obtained in 2010 and 2011, totaling nearly 8 and 1/2 days of Chandra time, did reveal the presence of X-ray emission. The X-ray brightness in 2000 and 2001 was about the same as or lower than in this deep image.
The new Chandra image of M83 is one of the deepest X-ray observations ever made of a spiral galaxy beyond our own.
The X-ray data provide important information about the nature of this explosion that astronomers think happened when a massive star ran out of fuel and collapsed. The distribution of X-rays with energy suggests that SN 1957D contains a neutron star, a rapidly spinning, dense star formed when the core of pre-supernova star collapsed. This neutron star, or pulsar, may be producing a cocoon of charged particles moving at close to the speed of light known as a pulsar wind nebula. The findings will appear in the Astrophysical Journal.
If this interpretation is confirmed, the pulsar in SN 1957D is observed at an age of 55 years, one of the youngest pulsars ever seen. The remnant of SN 1979C in the galaxy M100 contains another candidate for the youngest pulsar, but astronomers are still unsure whether there is a black hole or a pulsar at the center of SN 1979C.
Bibliographic information: Long et al. 2012. Recovery of the Historical SN1957D in X-rays with Chandra. Accepted for publication in ApJ; arXiv: 1207.1555v1