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Recent observations by PAMELA, Fermi-LAT, and AMS-02 have conclusivelyindicated a rise in the cosmic-ray positron fraction above 10 GeV, a featurewhich is impossible to mimic under the paradigm of secondary positronproduction with self-consistent Galactic cosmic-ray propagation models. Aleading explanation for the rising positron fraction is an additional source ofelectron-positron pairs, for example one or more mature, energetic, andrelatively nearby pulsars. We point out that any one of two well-known nearbypulsars, Geminga and Monogem, can satisfactorily provide enough positrons toreproduce AMS-02 observations. A smoking-gun signature of this scenario is ananisotropy in the arrival direction of the cosmic-ray electrons and positrons,which may be detectable by existing, or future, telescopes. The predictedanisotropy level is, at present, consistent with limits from Fermi-LAT andAMS-02. We argue that the large collecting area of Atmospheric CherenkovTelescopes (ACTs) makes them optimal tools for detecting such an anisotropy.Specifically, we show that much of the proton and gamma-ray background, whichaffects measurements of the cosmic-ray electron-positron spectrum with ACTs,may be controlled in the search for anisotropies. We conclude that observationsusing archival ACT data could already constrain or substantiate the pulsarorigin of the positron anomaly, while upcoming instruments (such as theCherenkov Telescope Array) will provide strong constraints on the source of therising positron fraction.

Probing the Pulsar Origin of the Anomalous Positron Fraction with AMS-02 and Atmospheric Cherenkov Telescopes