Cosmic ray positrons are known to be produced by interactions in the interstellar medium, but they might also originate in primary sources, such as pulsars, micro-quasars or through dark matter annihilation. Adriani et al. report that the positron fraction increases sharply over much of the energy range 1.5–100 GeV, which appears to be completely inconsistent with secondary sources—they therefore conclude that a primary source is necessary.
- O. Adriani
- G. C. Barbarino
- V. G. Zverev
