Pulsars as the Sources of High Energy Cosmic Ray Positrons

Hooper, Dan; Serpico, Pasquale Dario; Blasi, Pasquale

doi:10.1088/1475-7516/2009/01/025

Article
Report number	arXiv:0810.1527 ; FERMILAB-PUB-08-429-A ; CERN-PH-TH-2008-228 ; FERMILAB-PUB-08-429-A
Title	Pulsars as the Sources of High Energy Cosmic Ray Positrons
Author(s)	Hooper, Dan (Chicago U., Astron. Astrophys. Ctr. ; Fermilab) ; Blasi, Pasquale (Arcetri Observ. ; Fermilab ; Gran Sasso) ; Serpico, Pasquale Dario (CERN ; Fermilab)
Publication	2009
Imprint	10 Oct 2008
Number of pages	10
Note	Comments: 10 pages, 5 figures
In:	JCAP 01 (2009) 025
DOI	10.1088/1475-7516/2009/01/025
Subject category	Astrophysics and Astronomy
Abstract	Recent preliminary results from the PAMELA satellite indicate the presence of a large flux of positrons (relative to electrons) in the cosmic ray spectrum between approximately 10 and 50 GeV. As annihilating dark matter particles in many models are predicted to contribute to the cosmic ray positron spectrum in this energy range, a great deal of interest has resulted from this observation. Here, we consider pulsars (rapidly spinning, magnetized neutron stars) as an alternative source of this signal. After calculating the contribution to the cosmic ray positron and electron spectra from pulsars, we find that the spectrum observed by PAMELA could plausibly originate from such sources. In particular, a significant contribution is expected from the sum of all mature pulsars throughout the Milky Way, as well as from the most nearby mature pulsars (such as Geminga and B0656+14). The signal from nearby pulsars is expected to generate a small but significant dipole anisotropy in the cosmic ray electron spectrum, potentially providing a method by which the Fermi gamma-ray space telescope would be capable of discriminating between the pulsar and dark matter origins of the observed high energy positrons.
Copyright/License	Open Access

$The spectrum of cosmic ray positrons (left) and the positron fraction (right) resulting from the sum of all pulsars throughout the Milky Way. Also shown as a dashed line is the prediction for secondary positrons (and primary and secondary electrons in the right frames) as calculated in Ref.~\cite{moskalenkostrong}. In the right frames, the measurements of HEAT~\cite{heat} (light green and magenta) and measurements of PAMELA~\cite{Adriani:2008zr} (dark red) are also shown. We have used the injected spectrum reported in Eq.~(\ref{eq:inje}). In the lower frames, the upper (lower) dotted line represents the case in which the injection rate within 500 parsecs of the Solar System is doubled (neglected), providing an estimate the variance resulting from the small number of nearby pulsarscontributing to the spectrum.$ $The spectrum of cosmic ray positrons (left) and the positron fraction (right) resulting from the sum of all pulsars throughout the Milky Way. Also shown as a dashed line is the prediction for secondary positrons (and primary and secondary electrons in the right frames) as calculated in Ref.~\cite{moskalenkostrong}. In the right frames, the measurements of HEAT~\cite{heat} (light green and magenta) and measurements of PAMELA~\cite{Adriani:2008zr} (dark red) are also shown. We have used the injected spectrum reported in Eq.~(\ref{eq:inje}). In the lower frames, the upper (lower) dotted line represents the case in which the injection rate within 500 parsecs of the Solar System is doubled (neglected), providing an estimate the variance resulting from the small number of nearby pulsarscontributing to the spectrum.$ $The spectrum of cosmic ray positrons (left) and the positron fraction (right) resulting from the sum of all pulsars throughout the Milky Way. Also shown as a dashed line is the prediction for secondary positrons (and primary and secondary electrons in the right frames) as calculated in Ref.~\cite{moskalenkostrong}. In the right frames, the measurements of HEAT~\cite{heat} (light green and magenta) and measurements of PAMELA~\cite{Adriani:2008zr} (dark red) are also shown. We have used the injected spectrum reported in Eq.~(\ref{eq:inje}). In the lower frames, the upper (lower) dotted line represents the case in which the injection rate within 500 parsecs of the Solar System is doubled (neglected), providing an estimate the variance resulting from the small number of nearby pulsarscontributing to the spectrum.$ Show more plots

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