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Dimitrios Giannios “ High Energy Messengers ” Workshop, June 10th 2014

Is the IGM heated by TeV blazars?. Dimitrios Giannios “ High Energy Messengers ” Workshop, June 10th 2014 Sironi L. and Giannios D. 2014, ApJ, 787, 49; arXiv:1312.4538. TeV blazars. Cerenkov Telescopes: Blazars dominate the extragalactic TeV sky. (credit: TEVCat).

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Dimitrios Giannios “ High Energy Messengers ” Workshop, June 10th 2014

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  1. Is the IGM heated by TeV blazars? Dimitrios Giannios “High Energy Messengers” Workshop, June 10th 2014 Sironi L. and Giannios D. 2014, ApJ, 787, 49; arXiv:1312.4538

  2. TeV blazars Cerenkov Telescopes: Blazars dominate the extragalactic TeV sky (credit: TEVCat) • The blazar “sequence”: • a continuous sequence LBL - IBL - HBL • TeV blazars are dim (Ghisellini et al 11)

  3. TeV photons are absorbed in the IGM • TeV photons from blazars pair-produce in the IGM by interacting with ~ eV EBL photons. • mean free path is ~100 Mpc • The beam of electron-positron pairs has: • Lorentz factor γ=106-107 and density ratio α=10-15-10-18(wrt the IGM plasma) • These pairs should IC scatter off the CMB, producing ~ GeV photons. • mean free path is ~ 100 kpc (IC cooling length)

  4. No excess GeV emission from blazars Every TeV blazar should have a GeV halo of reprocessed light. However, not seen! (Neronov & Vovk 10)

  5. 1) IGM magnetic fields deflect the streaming pairs (Neronov & Vovk 10 …) intrinsic TeV spectrum Fermi upper limits absorbed TeV spectrum reprocessed GeV emission from pairs deflected by IGM fields (Tavecchio et al. 11) IGM fields or plasma instabilities? Every TeV blazar should have a GeV halo of reprocessed light. However, not seen! Two possibilities: 2) The pair energy is deposited into the IGM by plasma instabilities (Broderick, Chang, Pfrommer 12, 13)

  6. Two-stream (bump on tail) instability Oblique instability beam energy from particles to waves: → instability energy from waves to particles: → damping (Sironi & Giannios 14) Plasma instabilities in the IGM Interpenetrating beams of charged particles are unstable (beam-plasma instabilities) microscopic scales! Blazar-induced relativistic pairs IGM plasma collective limit

  7. IF the instability grows until all the beam energy is deposited into the IGM: • No reprocessed blazar GeV emission • IGM field estimates are invalid • IGM heating from blazars will have cosmological implications (Chang et al. 12) Beam-plasma linear evolution Linear analysis: the oblique instability grows 10-100 times faster than the IC cooling time. (Broderick et al. 12) The non-linear evolution of the beam-plasma system requires PIC simulations... Is the instability growing at the linear rate until it deposits all the beam energy into the IGM?

  8. What happens to TeV photons? ?

  9. No approximations, plasma physics at a fundamental level Tiny length and time scales need to be resolved  huge simulations, limited time coverage • Relativistic 3D e.m. PIC code TRISTAN-MP (Buneman ‘93, Spitkovsky ‘05) The PIC method • Particle-in-Cell (PIC) method: • Particle currents deposited on a grid • Electromagnetic fields solved on the grid via Maxwell’s equations • Lorentz force interpolated to particle locations Yee mesh

  10. Relaxation phase heating fraction B energy E energy In the end, the beam longitudinal dispersion ~0.2 γ, and the plasma heating fraction ~10% Cold beam: non-linear evolution Blazar-induced beams: Lorentz factor γ=106-107 and density ratio α=10-15-10-18 COLD beam with γ=300 and α=10-2 Exponential phase heating fraction The oblique instability grows fast, but it is quenched by self-heating of the beam

  11. IGM heating fraction (LS & Giannios 14) • COLD beams: • Regardless of the beam γ or α, the beam longitudinal dispersion reaches ~0.2 γ, and the IGM heating fraction ~10%. • Only 10% of the beam energy is deposited into the IGM, 90% is still available to power the reprocessed GeV emission. 10% in heat, 90% in GeV emission Blazar-induced beams: Lorentz factor γ=106-107 and density ratio α=10-15-10-18 Numerically tractable: Lorentz factor γ=101-103 and density ratio α=10-1-10-3

  12. in the presence of density inhomogeneities in the IGM. suppressed (Miniati et al 13) 10% in heat: a generous upper limit • The heating fraction can be ≪10%: • if the initial longitudinal beam dispersion is already > 0.2 γ. • if pre-existing magnetic fields are dispersing the beam sideways. → suppression

  13. The heating fraction can be ≪10%: • if the initial longitudinal beam dispersion is already > 0.2 γ. IGM heating fraction (Sironi & Giannios 14) Blazar beams are not cold • Blazar beams are born warm: • the pair production cross section peaks at ~ few mec2. • the TeV blazar spectrum and the EBL spectrum are broad. distance

  14. Is the IGM heated by TeV blazars? Not much.

  15. Long term beam-plasma evolution Beam-aligned electric field Magnetic energy beam beam z [c/ωp] z [c/ωp] x [c/ωp] x [c/ωp] y [c/ωp] y [c/ωp] (Sironi & Giannios, in prep.) • At the end of the relaxation phase, the beam-plasma system is still highly anisotropic, so still unstable (to the Weibel instability). • Blazar-induced pair beams might be a potential mechanism for generating small-scale (~ c/ωp ~ 108 cm) magnetic fields in cosmic voids?

  16. Summary • TeV photons from blazars will pair-produce in the IGM. The resulting electron-positron beam is unstable to the excitation of plasma instabilities. • Electrostatic plasma instabilities deposit ≪10% of the beam energy into the IGM. Most of the beam energy will result in GeV emission by IC scattering off the CMB. • After the saturation of electrostatic plasma instabilities, the beam is still anisotropic, and it might generate magnetic fields from scratch via the Weibel instability.

  17. Beam distribution function

  18. The complete evolution

  19. The complete evolution

  20. The complete evolution

  21. Dependence on the beam properties

  22. Dependence on the beam temperature

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