Speaker
Description
An excess of cosmic positrons above 10 GeV with respect to the spallation reaction of cosmic rays with the interstellar medium has been measured by AMS-02 with unprecedented precision. Recently, a gamma-ray halo in the direction of Geminga and Monogem pulsars has been detected by HAWC. These observations can be interpreted with positrons and electrons accelerated by pulsar wind nebulae (PWNe), released in a Galactic environment with a low diffusion and inverse Compton scattering (ICS) with the interstellar radiation fields.
We confirm the detection of a gamma-ray halo around Geminga analyzing almost 10 years of Fermi-LAT data above 8 GeV.
We inspect how the morphology of the ICS gamma-ray halos depends on the energy, the pulsar age and distance and the strength and extension of the low-diffusion bubble. In particular we demonstrate that gamma-ray experiments with a peak of sensitivity at about TeV energies are the most promising ones since, at these energies, the ICS halos are expected to be relatively small and the pulsar proper motion does not affect significantly the spatial morphology.
Then, we select a sample of PWNe reported in the HESS Galactic plane survey. Using the information available in this catalog for the gamma-ray spatial morphology, we find that the diffusion coefficient is two orders of magnitude smaller than the value considered to be the average in the Galaxy. Finally, we report the consequences for the contribution of PWNe to the positrons excess and for the propagation of these particles in the Galactic environment.
