Education

• 2017- 2021, MSc Electron-Positron beams in intergalactic medium
  with Yuri Lyubarsky

  Abstract/Description: Modern age Cerenkov telescopes discovered the strong emissivity of TeV gamma
  rays from blazars, active galactic nuclei which emit relativistic jets. In the
  intergalactic medium, ultra-high energy gamma rays interact with the extragalactic
  background light, producing electron-positron beams with the energies of
  100GeV - 10TeV. It has been suggested that due to the inverse Compton scattering
  upon the cosmic microwave background, these beams emit GeV photons giving
  rise to gamma-haloes around blazars. However, this prediction has been disproved
  by observations. One explanation for the disparity is the presence of an
  intergalactic magnetic field that deviates pairs from the line of site. Another
  possibility is that due to the two-stream instability, the pair beams lose energy on
  the excitation of plasma waves by resonance interaction. The last process has been
  studied intensively, both analytically and numerically, but conclusions are still
  controversial regarding the fate of the relativistic beams. We show that for the possible range of
  parameters of the extragalactic beams, the instability is strongly suppressed for all
  but quasi-perpendicular waves, due to inhomogeneity of the intergalactic medium.
  Hence the beam energy loss is negligible, while it mostly expands transversally.
  Therefore, the two-stream instability is unable to prevent the beam particles to
  produce the gamma halo via the inverse Compton scattering. The lack of the
  observed gamma haloes around blazars should be attributed to the extragalactic
  magnetic field.