The Origin Of Cosmic-ray Electrons

The origin of cosmic rays has long been an important project in astrophysics,while the origin of electrons/positrons is an important branch of this project.Due to synchrotron radiation and inverse Compton scattering,high-energy electrons/positrons would lose energy significantly during their propagation.Therefore,high-energy particles observed at the Earth should be produced by nearby sources.For CR electrons,it is commonly considered to be produced by supernova remnants in the Galaxy.While for positrons,there are many different models on their origin: generated as primary particles from pulsars or annihilated dark matter,or produced as secondary particles by hadronic interactions of primary cosmic rays.With the release of data from recent experiments like PAMELA,AMS-02,HESS and DAMPE,new features were detected on electron as well as positron spectra.One of the most attractive features among them is that the positron fluxes above 10 Ge V excess the prediction from our orthodoxy on galactic cosmic rays.These data with high precision extend to high energy,which constitute a challenge to the cosmic-ray standard model and provide opportunities for us to study the origin of CR electrons/positrons.Meanwhile,recent measurements of the extended gamma-ray emission around Geminga and PSR B0656+14 by HAWC suggested that there are inefficient diffusion regions surrounding these two pulsars,where the diffusion coefficient is two magnitude smaller than that in the ISM.This observation offer a new perspective to study cosmic rays.Motivated by that,we try to explain the electron/positron fluxes we detected through astrophysical origins.In Chapter 1,we briefly introduce the backgrounds on galactic electrons/positrons,including the standard model of galactic cosmic rays,observational experiments to de-tect electrons/positrons and recent observational data,as well as popular models to explain the origins of cosmic-ray electrons/positrons.In Chapter 2,motivated by the HAWC observations,we assume an inefficient diffusion regions around Vela X while outside is the region with normal diffusion coefficient.We develop an analytic approach method to solve this two-zone diffusion problem.We use the recent HESS data to constrain the diffusion coefficient around Vela X,which we find is two magnitude smaller than the standard one.In Chapter 3,we use the DRAGON code to examine the possibility that all of the positrons can explained by secondary production scenario.When fitting to the proton and antiproton data,the corresponding positron flux cannot explain the AMS-02 observations because of significant cooling.Hence primary positrons from other sources are needed.In Chapter 4,we consider the two-zone diffusion model in the case of Geminga and PSR B0656+14.By fitting the upper limit in the Ge V energy range from Fermi-LAT and the Te V fluxes from HAWC,we test whether these two pulsars can contribute a dominant part to the positron excess.In the last Chapter,we make conclusions and make a prospective to the future work.