Positron Excess from Cosmic Ray Interactions in Galactic Molecular Clouds

Abstract

The recent data on cosmic ray positron flux measured near the Earth by the \\textit{Alpha Magnetic Spectrometer} (AMS-02) experiment extends to TeV energy. The positron flux measured in GeV$^2$ m$^{-2}$ sec$^{-1}$ sr$^{-1}$ rises with energy and shows a peak near a few hundred GeV. This rising positron flux cannot be explained by interactions of cosmic rays with interstellar hydrogen gas. Due to the progress in multi-wavelength astronomy, many new Galactic Molecular Clouds (GMCs) have been discovered in our Galaxy recently. We use the updated list of GMCs, which are distributed in the Galactic plane, to find the secondary positrons produced in them in interactions of cosmic rays with molecular hydrogen. Moreover, by analysing the Fermi LAT data, new GMCs have been discovered away from the Galactic plane. We also include some of these GMCs closest to the Earth where cosmic ray interactions are producing secondaries. After including these GMCs we show that the positron excess can be mostly well explained, with a small contribution from unknown extra component near the peak.