Emission of cosmic rays from Pulsar wind nebulae

Abstract

The goal of the paper is to interpret AMS-02 positron data. Most of the positrons come from secondary production which can fit well the data below 10 GeV. However, above 10 GeV the positron flux detected is much higher than the predictions for the secondary production. This is called ‘positron excess’ whose origin remains unknown, and interpretations including supernova remnants, pulsar wind nebulae (PWNe) or dark matter have been considered. In this paper, we investigate if PWNe can explain this ‘positron excess’ and whether a single pulsar can contribute entirely to it. To do this, we select some powerful pulsars in the ATNF Pulsar Catalogue with specific age and distances from earth and calculate their positron flux. By using a minimization package in Python to adjust the spectral slope of the PWNe and the normalization of the secondaries, we find the best fit to AMS-02 data for each of those pulsars. We can see from the result that if we want to explain the ‘positron excess’ using a single pulsar, Geminga is the best solution in the ATNF Pulsar Catalogue. Moreover, we find that except for the powerful pulsar J0633+1746 (Geminga), B1742-30 and J1741-2054, most of the pulsars we selected need an efficiency much greater than 1 to fit the data. It means that for those pulsars, one pulsar’s energy is not powerful enough to explain the data entirely. Therefore, for pulsars that are not powerful enough, adding more pulsars together provides us with a possible way to interpret this ‘positron excess’ problem.