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The Pair-halo Effect

The Pair-halo Effect. By Brian Baughman. Introduction. Brief overview of pair-halo effect Scientific possibilities Pair production Synchrotron cooling Compton up-scattering Observational concerns. Outline. Compton Up-scattered Photon. Original Source Photon. CMB Photon.

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The Pair-halo Effect

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  1. The Pair-halo Effect By Brian Baughman

  2. Introduction • Brief overview of pair-halo effect • Scientific possibilities • Pair production • Synchrotron cooling • Compton up-scattering • Observational concerns Outline

  3. Compton Up-scattered Photon Original Source Photon CMB Photon Magnetic Field e+/- pair Original Source Photon EBL Photon The pair-halo effect Gamma Source

  4. The pair-halo effect • The Extra-Galactic Magnetic Field (EMF) has yet to be thoroughly probed • Theories give predictions for the magnitude ranging from 10^-6 to 10^-19 gauss • Theories for the formation and consequences of the EMF are just as diverse. Probing the Extra-Galactic Magnetic Field

  5. The pair-halo effect • Extra-Galactic Background Light (EBL) is a probe of cosmology • An accurate map of the evolution of EBL can help pin down various cosmological models • Observation of the Pair-halo effect can provide a red shift (z) dependent measurement of the EBL Indirect observation of Extra-Galactic Background Light

  6. The pair-halo effect • TeV gammas preferentially pair produce off infra-red and optical photons Gamma Gamma t http://www.phys.ualberta.ca/~gingrich/phys512/latex2html/node103.html

  7. The pair-halo effect • (IR) spectrum to the left (Primack et. Al, 1999) • Other models for the EBL exist Gamma Gamma

  8. The optical depth to the right show how high energy gammas will quickly pair produce off of this EBL model The pair-halo effect • Gammas above the red line will likely convert before reaching us. • The converted gammas’ daughter products may be observable through the pair-halo effect Gamma Gamma (Primack et. Al, 1999)

  9. The pair-halo effect • High Energy e+/- up-scatter Cosmic Microwave Background photons Compton Up-scattering t http://www.phys.ualberta.ca/~gingrich/phys512/latex2html/node102.html

  10. The pair-halo effect • The plot to the right shows the energy loss rate due to Compton scattering of e+/- pairs. • The cooling time for energies of interest are very short. Compton Cooling Plot from Sangjin Lee et. al, ApJ 455 :L21–L24, 1995 December 10

  11. The pair-halo effect • As the pairs travel through the EMF deflection occurs of the order: • q= (d/l)1/2 l/RL • d = distance traveled before Compton up-scattering • RL = Lamor radius • l = Correlation length of EMF • If RL < the Compton cooling length and l is small then the pairs can become isotropic Pair Deflection

  12. The pair-halo effect • A multitude of variables go into determining the observable range of this effect with a given detector • The phase space is not orthogonal and thus must be studied as a multi-dimensional system • The optical depth() for gammas due to pair-production • The e+/- pair energy loss rate • The magnitude and correlation of the Extra-galactic Magnetic Field (EMF) • The source spectrum Relevant scales Distance to source

  13. The pair-halo effect • Observation of the pair-halo effect will depend on an experiment’s ability to differentiate between a true point source and an extended source • Similar distortions from the standard point-spread function (PSF) will occur with energy dependence different from the instrument response Observational Concerns

  14. The pair-halo effect • If the EMF is correlated close to a given source we expect the source to be elongated along the • Large scale correlations in the EMF would be observable correlated elongation of nearby sources EMF

  15. The pair-halo effect • Various models for Initial Mass Function in galaxy formation give very different results for the opacity of the early universe thus if probing the red shift dependence of the pair-halo effect could help choose the correct model • Different models for cold dark matter also produce different opacities as well. Thus different energy dependencies EBL

  16. The pair-halo effect • Observation of the pair-halo effect could shed light on the formation of the Extra-galactic magnetic field • The pair-halo effect my be used as a secondary probe of the EBL, in conjunction with extinction studies. • The signature of the pair-halo effect will make observation difficult Conclusions

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