Annihilation radiation from thermal electron-positron plasma on the ground Landau level: The case of low magnetic fields

A. D. Kaminker, George Pavlov, P. G. Mamradze

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Abstract

The intensity and polarization of two-photon annihilation in a magnetic fuield B≪Bcr=4.4×1013 G are studied in detail for a, one-dimensional thermal distribution of annihilating electrons and positrons on the ground Landau level. With the increase of temperature T the total annihilation rate and energy losses decrease, being higher than for the isotropic thermal distributions at the same T. The shapes of intensity spectra at sin ρ{variant}=0 (ρ{variant} is the angle between B and wave-vector) are close to those in the isotropic case. The widths and blue-shifts of the spectra decrease with increasing sin ρ{variant} and increase with increasing T. Logarthmic singularities arise in the spectra at E»mc2/sin ρ{variant}. Power-like parts are formed in the wings of the spectra for kT≫mc2 and not too small sin ρ{variant}. The direction-integrated spectra reach their (finite) maxima, at E=mc2 for any T. The radiation concentrates near the plane, perpendicular to the magnetic field for E close to mc2 and is beamed along the magnetic field for E far from mc2. Energy-integrated angular distributions are stretched along B, the stronger the higher T. The rediation is linearly polarized in the plane formed by the magnetic field and weve-vector. Typical values of the polarization inside the cores of the annihilation spectra are ∼(kT/mc2) sin ρ{variant} and [ln (kT/mc2)]-1 for kT≪mc2 and kT sin ρ{variant}≫mc2, respectively. Annihilation radiation dominates over Bremsstrahlung in the e plasma at kT≲7 mc2. The results are useful for interpretation of the annihilation radiation in the gamma-ray bursts. They permit to estimate temperature, gravitational potential, and emission measure of radiating regions and the beaming of the radiation.

Original languageEnglish (US)
Pages (from-to)241-284
Number of pages44
JournalAstrophysics and Space Science
Volume174
Issue number2
DOIs
StatePublished - Dec 1 1990

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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