Bifurcation in first-order fermi acceleration and the origin of cosmic rays

2007 ◽  
pp. 287-301
Author(s):  
M. A. Malkov
Keyword(s):  
Cosmic Rays ◽  
Fermi Acceleration ◽  
First Order

scholarly journals Non-thermal emission from cosmic rays accelerated in H II regions

2019 ◽  
Vol 630 ◽  
pp. A72 ◽  
Author(s):  
Marco Padovani ◽  
Alexandre Marcowith ◽  
Álvaro Sánchez-Monge ◽  
Fanyi Meng ◽  
Peter Schilke
Keyword(s):  
Cosmic Rays ◽  
Thermal Radiation ◽  
Thermal Emission ◽  
Cosmic Ray ◽  
Local Source ◽  
Relativistic Electrons ◽  
Deep South ◽  
Fermi Acceleration ◽  
First Order ◽  
Order Of Magnitude

Context. Radio observations at metre-centimetre wavelengths shed light on the nature of the emission of H II regions. Usually this category of objects is dominated by thermal radiation produced by ionised hydrogen, namely protons and electrons. However, a number of observational studies have revealed the existence of H II regions with a mixture of thermal and non-thermal radiation. The latter represents a clue as to the presence of relativistic electrons. However, neither the interstellar cosmic-ray electron flux nor the flux of secondary electrons, produced by primary cosmic rays through ionisation processes, is high enough to explain the observed flux densities. Aims. We investigate the possibility of accelerating local thermal electrons up to relativistic energies in H II region shocks. Methods. We assumed that relativistic electrons can be accelerated through the first-order Fermi acceleration mechanism and we estimated the emerging electron fluxes, the corresponding flux densities, and the spectral indexes. Results. We find flux densities of the same order of magnitude of those observed. In particular, we applied our model to the “deep south” (DS) region of Sagittarius B2 and we succeeded in reproducing the observed flux densities with an accuracy of less than 20% as well as the spectral indexes. The model also gives constraints on magnetic field strength (0.3–4 mG), density (1–9 × 104 cm−3), and flow velocity in the shock reference frame (33–50 km s−1) expected in DS. Conclusions. We suggest a mechanism able to accelerate thermal electrons inside H II regions through the first-order Fermi acceleration. The existence of a local source of relativistic electrons can explain the origin of both the observed non-thermal emission and the corresponding spectral indexes.

FIRST-ORDER DISTRIBUTED FERMI ACCELERATION OF COSMIC RAY HADRONS IN NON-UNIFORM MAGNETIC FIELDS

2009 ◽  
Vol 24 (19) ◽  
pp. 1461-1472 ◽  
Author(s):  
R. SCHLICKEISER
Keyword(s):  
Magnetic Field ◽  
Cosmic Rays ◽  
Large Scale ◽  
Cosmic Ray ◽  
Acceleration Process ◽  
Fermi Acceleration ◽  
Helicity State ◽  
First Order ◽  
Physical Mechanisms ◽  
Guide Magnetic Field

Large-scale spatial variations of the guide magnetic field of interplanetary and interstellar plasmas give rise to the adiabatic focusing term in the Fokker–Planck transport equation of cosmic rays. As a consequence of the adiabatic focusing term, the diffusion approximation to cosmic ray transport in the weak focusing limit gives rise to first-order Fermi acceleration of energetic particles if the product HL of the cross helicity state of Alfvenic turbulence H and the focusing length L is negative. The basic physical mechanisms for this new acceleration process are clarified and the astrophysical conditions for efficient acceleration are investigated. It is shown that in the interstellar medium this mechanism preferentially accelerates cosmic ray hadrons over 10 orders of magnitude in momentum. Due to heavy Coulomb and ionization losses at low momenta, injection or preacceleration of particles above the threshold momentum pc≃0.17Z2/3 GeV /c is required.

scholarly journals Comment on the first-order Fermi acceleration at ultra-relativistic shocks

2002 ◽  
Vol 394 (3) ◽  
pp. 1141-1144 ◽  
Author(s):  
M. Ostrowski ◽  
J. Bednarz
Keyword(s):  
Fermi Acceleration ◽  
First Order ◽  
Relativistic Shocks

First-order Fermi acceleration in solar flares as a mechanism for the second-step acceleration of prompt protons and relativistic electrons

1983 ◽  
Vol 267 ◽  
pp. 433 ◽  
Author(s):  
T. Bai ◽  
H. S. Hudson ◽  
R. M. Pelling ◽  
R. P. Lin ◽  
R. A. Schwartz ◽  
...  
Keyword(s):  
Solar Flares ◽  
Second Step ◽  
Relativistic Electrons ◽  
Fermi Acceleration ◽  
First Order
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