The millisecond pulsar contribution to the rising positron fraction
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Date
2016Author
Venter, Christo
Kopp, Andreas
Büsching, Ingo
Harding, Alice K.
Gonthier, Peter L.
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Pair cascades from millisecond pulsars (MSPs) may be a primary source of Galactic electrons and
positrons that contribute to the increase in positron flux above 10 GeV as observed by PAMELA
and AMS−02. The Fermi Large Area Telescope (LAT) has increased the number of detected γ-ray
MSPs tremendously. Light curve modelling furthermore favours abundant pair production in MSP
magnetospheres, so that models of primary cosmic-ray positrons from pulsars should include
the contribution from the larger numbers of MSPs and their potentially higher positron output
per source. We model the contribution of Galactic MSPs to the terrestrial cosmic-ray electron /
positron flux by using a population synthesis code to predict the source properties of presentday MSPs. We simulate pair spectra assuming an offset-dipole magnetic field which boosts pair
creation rates. We also consider positrons and electrons that have additionally been accelerated to
very high energies in the strong intrabinary shocks in black widow (BW) and redback (RB) binary
systems. We transport these particles to Earth by calculating their diffusion and the radiative
energy losses they suffer in the Galaxy using a model. Our model particle flux increases for nonzero offsets of the magnetic polar caps. We find that pair cascades from MSP magnetospheres
contribute only modestly around a few tens of GeV to the measured fluxes. BW and RB fluxes
may reach a few tens of percent of the observed flux up to a few TeV. Future observations should
constrain the source properties in this case.
URI
http://hdl.handle.net/10394/32138https://pos.sissa.it/236/462/
https://doi.org/10.22323/1.236.0462