COSMIC-RAY POSITRONS FROM MILLISECOND PULSARS

Journal Article · Fri Jul 10 04:00:00 EDT 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/807/2/130· OSTI ID:22522192

Venter, C.; Kopp, A.; Büsching, I. ^[1]; Harding, A. K. ^[2]; Gonthier, P. L. ^[3]

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1. Centre for Space Research, North-West University, Potchefstroom Campus, Private Bag X6001, Potchefstroom 2520 (South Africa)
2. Astrophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
3. Hope College, Department of Physics, Holland, MI (United States)

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 new MSPs, 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.

• OSTI ID: 22522192
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 807; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
COSMIC ELECTRONS
COSMIC NEUTRONS
COSMIC POSITRONS
DIAGRAMS
DIFFUSION
DIPOLES
ENERGY LOSSES
GALAXIES
GEV RANGE
NEBULAE
PAIR PRODUCTION
PULSARS
RUTHERFORD BACKSCATTERING SPECTROSCOPY
STARS
STELLAR MAGNETOSPHERES
STELLAR WINDS
TELESCOPES
TEV RANGE
VISIBLE RADIATION