A supernova accelerator?

5 June 2002

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The origin of cosmic rays - high energy particles from outer space - has puzzled physicists since their discovery in 1912. Now researchers using the CANGAROO-II observatory have reported detecting cosmic gamma rays striking the Earth’s atmosphere from the direction of a supernova remnant, RXJ1713.7-3946. The energy spectrum of the gamma rays is explained well in terms of the decay of particles called pions, presumably produced in the collisions of high-energy protons accelerated in the supernova shock waves. This provides evidence supporting the theory that cosmic rays, except for those of the highest energies, originate from supernova remnants. This image is a map of RXJ1713.7-3946 centred on the region that is brightest in energetic X-rays (detected by X-ray satellites) - the black contours show the X-ray emission. The map shows the statistical significance of gamma-rays detected with energies in the TeV range detected by CANGAROO, with the red regions at the centre the most significant. (The vertical axis is relative declination, the horizontal axis right ascension. The black circle shows the spread expected from a point source; the area of greater significance (yellow to red) extends beyond this towards a region that is bright in X-rays.)

Credit: CANGAROO

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