Cosmic-ray positrons from millisecond pulsars

View/ Open
Date
2015Author
Venter, C.
Kopp, A.
Büsching, I.
Harding, A.K.
Gonthier, P.L.
Metadata
Show full item recordAbstract
Observations by the Fermi Large Area Telescope of γ-ray millisecond pulsar (MSP) light curves imply copious pair
production in their magnetospheres, and not exclusively in those of younger pulsars. Such pair cascades may be a
primary source of Galactic electrons and positrons, contributing to the observed enhancement in positron flux above
∼10 GeV. Fermi has also uncovered many newMSPs, impacting Galactic stellar population models.We investigate the
contribution of Galactic MSPs to the flux of terrestrial cosmic-ray electrons and positrons. Our population synthesis
code predicts the source properties of present-day MSPs. We simulate their pair spectra invoking an offset-dipole
magnetic field. We also consider positrons and electrons that have been further accelerated to energies of several TeV by
strong intrabinary shocks in black widow (BW) and redback (RB) systems. Since MSPs are not surrounded by pulsar
wind nebulae or supernova shells, we assume that the pairs freely escape and undergo losses only in the intergalactic
medium. We compute the transported pair spectra at Earth, following their diffusion and energy loss through the
Galaxy. The predicted particle flux increases for non-zero offsets of the magnetic polar caps. Pair cascades from the
magnetospheres of MSPs are only modest contributors around a few tens of GeV to the lepton fluxes measured by the
Alpha Magnetic Spectrometer, PAMELA, and Fermi, after which this component cuts off. The contribution by BWs and
RBs may, however, reach levels of a few tens of percent at tens of TeV, depending on model parameters
URI
http://hdl.handle.net/10394/18444https://doi.org/10.1088/0004-637X/807/2/130
http://iopscience.iop.org/article/10.1088/0004-637X/807/2/130