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Gamma-rays from Supernovae and Supernova Remnants

A supernova, the tremendous explosion that ends the "normal" life of a star, is a great laboratory for gamma-ray astronomy. The study of how a star evolves and eventually explodes, leaving behind a neutron star or black hole is interesting. For the gamma-ray astronomer, however, it is what happens after the star lives its normal life which is worth watching. The collapse of the massive star's core when it has spent its nuclear fuel results in a tremendous explosion. This explosion is a factory for creating heavy elements and it is the decay of these elements which is of interest to gamma-ray astronomers.

Large Magellanic Cloud before and after SN 1987a

For instance, one of the most famous supernovae - SN 1987A - emits gamma-ray photons from the decay of radioactive 56Co. As the remnant of the supernova ages, different elements become dominant in the gamma-ray radiation. The supernova remnant known as Cas A is a source of gamma-ray line emission (at 1.16 MeV) from the decay of 44Ti. At an age of around 300 years, Cas A is old compared to SN 1987A but young as far as most supernova remnants go.

Compton Telescope image of Cas A
Comptel image of Cas A
As remnants age, the radioactive emissions are greatly reduced but there may still be gamma-rays to explore. The remnant could be the site of particle acceleration with these relativistic particles creating gamma-rays through collisions with surrounding matter. There is some statistical evidence that the unidentified gamma-ray sources may be associated with supernova remnants, although what the association is remains unclear. It could be that the remnants are actually just obscuring gamma-ray pulsars, or it could be that the emission is coming from the remnant itself. Future gamma-ray instruments, with greater sensitivity, are required to further understand the role supernova remnants play in both the creation of the matter we see in the Universe, and the role they play in the galactic gamma-ray emission.

Imagine the Universe is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center.

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