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.
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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. |
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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.
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