Primary cosmic rays, which are produced outside the solar

system are mainly protons and alpha particles. But suppose

we have some positrons in primary cosmic rays.

Positron photon scattering cross section is also energy dependent. A

result which can be derived using quantum field theory. As the

cosmic ray positrons travel towards earth, they are also scattered by

photons of Cosmic microwave background, which is present

everywhere in the universe. If the energy of the cosmic ray positron

is above a certain threshold limit then they will not reach

earth, so they will be cut-off.

But I suppose the fraction of positrons in cosmic rays is very small.

Biswajoy, thanks, but most of your response is sort of repetition of what I wrote in my detailed explanation of my question. If you have any data as to cutoff for specifically electrons (or positrons), I'd appreciate that.

I was referring to positrons. I guess electrons are lost from the

nuclei during their passage. For non-technical information you

can see NASA website, http://helios.gsfc.nasa.gov/gcr.html

I have never worked on cosmic ray Physics myself.

Biswajoy, thanks for your pointer.

Hi Alexander,

The upper limit of cosmic ray (CR) electrons should be about 1-2 TeV due to unavoidable synchrotron radiation and inverse Compton scattering. Moreover, from the diffusion models of Galactic CR transport stems a local origin (pulsars, SNRs at distance

Dear Samvel,

Great thanks for your straight to the point info and sources! Will be reading those papers very thoroughly. It is always a pleasure to have such a highly expert advice...

There are secondary electrons/positrons in extragalactic space, which are generated via interactions of primary cosmic protons with cosmic microwave background radiation. (These interactions give rise to GZK-limit.) Secondary electrons have energies in the range 1.5*10^(14) – 6*10^(19) eV, depending of the primary proton energy and of the kinematics of proton interaction. These secondary electrons propagate through space loosing energy due to: 1) Compton scattering on background radiation, 2) synchrotron radiation in extragalactic magnetic fields. However in the Compton scattering the electron energy is carried through the space (because the positron turns into gamma-quantum which in turn generates an electron/positron pair and so on, and in this cycle one of the particles has the initial electron energy). Synchrotron radiation does not stop electron energy carrying if magnetic fields are less than 10^(-9) Gs, which coincides with the upper limit on the extragalactic magnetic field. So in the extragalactic space electrons/positrons exist at energies up to 6*10^(19) eV. However in the Galaxy they lose energy because the galactic magnetic field is about 10^(-6) Gs .

Hi, Dr. Uryson,

great thanks for the details! I am a bit familiar with GZK-limit for protons, as well as with Compton scattereing of electroms at CMB. A new complicationg factor to me is that fast electrons can loose a lot of energy "locally", i. e. in the Galaxy. Would it be big trouble for you to supply me with a pointer to a recent review on the subject (preferably about the whole thing...)

PS. Wow! FIAN isn't empty yet....-)

Hi, Alexander,

data on galactic electrons/positrons are obtained in experiments:

AMS-02 (the Alfa Magnetic Spectrometer Experiment), PAMELA (a Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics). Papers with spectra and discussion etc. by AMS-02 and PAMELA are available on their official websites and here:

www.ams02.org

AMS-02 » Archive » New results from AMS presented at ICRC 2013

Besides, AMS-02 data are discussed in

CERN Courier, Sep 27, 2013 “AMS-02 provides a precise measure of cosmic rays”.

Regards

Anna Uryson

P.S. FIAN is not totally empty but “reorganization”(=liquidation) is declared.

Dear Anna,

Somehow I missed your reply of Feb. 2014. My belated thanks!

Best regards

-- Alex Kaplan