Cosmic ray in the Galaxy

Another, linearly polarized, radio source in the Crab nebula, where a supernova explosion was observed in the year 1054, leaving behind a pulsating neutron star, could be of similar origin as the radiation in the Milky Way. The likelihood that the pulsar drives the acceleration of both relativistic electrons and of cosmic rays could imply that most cosmic rays in the Galaxy are also... 

Fig. 9.7. Evolution of Be and B abundances according to the model based on confinement of cosmic rays in the early Galaxy (solid curves). Some observational data points are shown with error bars. Adapted from Prantzos, Casse and Vangioni-Flam (1993).

The mathematical description of the propagation of cosmic rays through the galaxy usually assumes dynamic equilibrium between production of a cosmic ray species either by acceleration in a source (primary cosmic rays), or by spallation of a parent species in the ISM (secondary cosmic rays), and loss by diffusion or convection, energy loss, radioactive decay, or spallation (e.g. [10]). Many of the parameters in the balance equation, in particular diffusion coefficients and boundary conditions, are poorly known. For our discussion here, we grossly simplify the situation Instead of dealing with a diffusion co-... 

Fig. 9.2. Schematic view of the life history of a cosmic ray from acceleration in the source through propagation in the Galaxy to observation above the Earth s atmosphere. Adapted from Rolfs and Rodney (1988).

In order to reconstruct relative abundances of these nuclei at source, we must first expurgate all the fragmentation debris. This is done with the help of a model to be described shortly. The Galaxy is not totally closed as regards cosmic ray movements. Three dangers await any particle launched at high speed in the Galaxy ... 

Abstract We present the observational evidence and the theoretical indications for the presence of relativistic particles (cosmic rays) in galaxy clusters. We discuss the basic ideas for their origin and explore the astrophysical techniques to unveil their nature. 

Figure 16.23. Two examples of neutralino models that provide a good fit to the excess of cosmic ray positrons observed by the HEAT collaboration. The two sets of data points (open and filled squares) are derived from two different instruments flown in 1994-95 and 2000. The lines represent (i) the best expectation we have from models of cosmic ray propagation in the galaxy ( bkg. only fit ), which underestimate the data points above 7 GeV (ii) the effect of adding positrons from neutralino annihilations (lines SUSY component , SUSY+bkg. fit , and bkg. component , the latter being the resulting background component when the data are fitted to the sum of background and neutralino contributions). (Figures from Baltz, Edsjo, Freese, Gondolo(2002)).

To a first approximation, the all-particle spectrum of cosmic rays can be described by a power law on more than 11 decades on particle energy, so that the dependence of cosmic ray intensity on particle energy is close to E 2-7 at energy more than about 10 GeV. Closer examination reveals some structure in the galactic cosmic ray spectrum that includes the knee at 4 x 1015 eV, the second knee at about 1018 eV, and the ankle at 1019 eV. The steady-state spectrum is shaped by two principle processes - the acceleration at the sources and the subsequent propagation in the Galaxy. 

If one uses the cosmic ray energy requirements and the nonthermal radiation as a guideline, then the most powerful accelerators of relativistic particles in the Galaxy should be supernovae and supernova remnants, pulsars, neutron stars in close binary systems, and winds of young massive stars. The total power Lcr needed to maintain the observed energy density of cosmic rays is estimated as 1041 erg/s. For the acceleration by a supernovae, this estimate... 

It is worth noting that the knee observed in the cosmic ray spectrum at 4 x 1015 eV may arise not in the sources but in the process of cosmic ray propagation in the Galaxy, e.g. as a result of interplay between ordinary and Hall diffusion in galactic magnetic fields [54], [Roulet 2004], Of course, this explanation requires the existence of a power-law source spectrum which extends without essential breaks up to about 1018 eV or even further. 

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