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Ultrahigh-energy gammas and SN 1987A.

Ultrahigh-energy gammas and SN 1987A

Astrophysicists have expected that supernovas would be sources of what they call ultrahigh-energy gamma rays. These are gamma rays with the highest energies ever detected from natural sources, 10.sup.14 electron-volts and higher. Theorists have proposed that protons accelerated in the supernova explosion would produce these gamma rays by interacting with other matter in the neighborhood. Such high-energy protons are the most common objects among the cosmic rays, and many astrohysicists have thought that supernovas ought to be an important source of them.

Gamma rays of lower energy (around 1 million or 10.sup.6 electron-volts) have been recorded from SN 1987A (SN:1/2/88, p.5). These low-energy gamma rays apparently come from processes in the supernova that make the heavier chemical elements. However, the ultrahigh-energy ones, supposedly produced by cosmic ray protons, have not appeared, though a group from the University of Adelaide, Australia, searched six months of records for evidence of them.

In the March 1 ASTROPHYSICAL JOURNAL LETTERS, D. Ciampa, D.J. Bird. R.W. Clay, P.G. Edwards and R.J. Protheroe state that their installation in Buckland Park, South Australia, is probably the only one located so as to be able to record showers caused by gamma rays from SN 1987A. It is an array of sensors laid out to record showers of particles triggered by the ultrahigh-energy gamma rays as they hit the atmosphere. Because the first six months after the appearance of the supernova yielded nothing, the observers say they can set rather low limits on the amount of high-energy protons produced in the supernova and their interactions with other matter in the area.
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Title Annotation:supernova 1987A
Publication:Science News
Date:Mar 12, 1988
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