Constraints on cosmic-ray positron excess and average pulsar parameters

Abstract

Recent, accurate e+/(e++e-) ratio measurements in cosmic rays allow us to distinguish among different estimates of secondary positron production in the interstellar medium (ISM), provided the effect of solar modulation and solar polarity are properly taken into account. Data above a few GeV indicate that a possible extra component of positrons could be required in addition to the secondaries. This positron excess is compatible with the hypothesis of pair production at the polar cap of mature pulsars. Assuming only pulsar contributions without any exotic contributions such as dark-matter annihilation, the average parameters of Galactic pulsars contributing to positron and electron interstellar fluxes were obtained. These parameter values are found near the peak of the distributions of the observed characteristics of radio pulsars. The studied gamma-ray pulsar sample is too small to make any conclusion. The expected e+/(e++e -) ratio from the PAMELA experiment currently in orbit is reported in this paper. The GLAST mission will allow us to double-check our findings about the role of pair production at the pulsar polar cap and outer gap. © ESO 2007.