Electrons and Positrons in Cosmic Rays

Abstract

This review concentrates on the results obtained, over the last ten years, on the astrophysics of high-energy cosmic ray electrons and positrons. The anomalies, observed in the data of recent experiments (possible bump in the electron spectrum and the PAMELA anomaly in the positron fraction) are discussed through the systematic use of simple analytical solutions of the transport equations for cosmic ray electrons. Three main ways of explaining the origin of the anomalies are considered: the conservative way supposing the positrons to be pure secondary particles; the nearby sources like pulsars origin; and the dark matter origin. This review discusses, also, the inability to select the pulsars model or the dark matter model to explain the electron anomalies on the basis of the electron spectra with the usual large energy binning ( 15%). It is argued that the signature of nearby pulsars origin of the anomalies against the dark matter origin could be the fine structure of the cosmic ray electron spectrum predicted in the Malyshev et al. paper (2009) and which was observed in the data from the high-resolution ATIC experiment (2009)(2010)(2011). To date, the high-resolution ATIC data was the only experimental result of this type published in the literature. Therefore, they should be tested by other experiments as soon as possible. Generally, there is, also, rather controversial situations between the data of the majority of recent experiments and, consequently, there is a noted urgent need for new high-precision and high-statistical experiments.

Cosmic ray signatures of a 2–3 Myr old local supernova

“…The low-energy component F (1) (R) representing the average CR flux from sources in the disk is modified by energy losses as F (1) (R) → F (1) (R)(E/E 0 ) 0.5 [29]. In Fig.…”

Positive charge prevalence in cosmic rays: Room for dark matter in the positron spectrum

“…Although the interpretations of the positron anomaly often appear plausible (see, e.g., [23,54] for a review), they do not form one cohesive picture. The problem seems to be that very different models fit the data equally well.…”

Structures in the cosmic ray energy spectra

“…Finally, with respect to positrons, a number of observations have reported an upturn in the positron fraction ( the number of positrons divided by that of electrons plus positrons ), starting at about 5 GeV [2,3,4,5,6]. The comprehensive list of references can be found in the review [7]. The case here for a local source providing the extra positrons seems overwhelming.…”

“…As remarked already, the lower energy region is the province of solar modulation, which is known to be dependent on the charge sign of the CR and on the time of observation, by way of the solar magnetic field polarity [eg [15]]. The difference between the positron fraction measured by AMS-01 [16] and PAMELA [2] in the different periods of solar activity can be caused by this phenomenon [7].…”