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gg Absorption and Pair Production

gg Absorption and Pair Production. gg Absorption and Pair Production. 0. Threshold energy e thr of a g -ray to interact with a background photon with energy e 1 :. 2. e thr = . e 1 (1 – cos q ). e +. e -. q. e pk ~ 2/ e 1. e g. e 1. gg Absorption.

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gg Absorption and Pair Production

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  1. gg Absorption and Pair Production

  2. gg Absorption and Pair Production 0 Threshold energy ethr of a g-ray to interact with a background photon with energy e1: 2 ethr = e1 (1 – cosq) e+ e- q epk ~ 2/e1 eg e1

  3. gg Absorption Delta-Function Approximation: VHE gamma-rays interact preferentially with IR photons:

  4. Spectrum of the Extrgalactic Background Light (EBL) Starlight Dust (Finke et al. 2010)

  5. EBL Absorption (Finke et al. 2010)

  6. gg Absorption Intrinsic to the Source Importance of intrinsic gg-absorption is estimated by the Compactness Parameter: Radiation Transfer Equation gives: Fnint if tgg « 1 ≈ Fnint/tgg if tgg » 1

  7. gg-Absorption Internal to the Source Break in the g-ray spectrum at (or beyond) energy eg → Limit on Doppler factor! eg nFn ~ n1-ax eg-ag Fn 2/eg eg-(ag + ax) tgg « 1 → tgg (eg) ~ egax tgg » 1 eg

  8. Pair Production Spectrum Simplest approximation: g+ = g- = (e1 + e2)/2 (e0 = 2g) Interaction of two power-law photon spectra with indices a = 1.5

  9. Pair Cascades • The produced e+/e- may have enough energy to radiate new g-rays (Compton), possibly with enough energy to be subject to gg-absorption + pair production … • (Deflected) IC cascades may be detectable in GeVg-rays, lead to extended halos -> Limits on B-field

  10. Magnetic-Field Limits 1ES 0229+200 (z=0.14) 1ES 1218+304 (z=0.182) RGB J0710+591 (z=0.13) Cascade IC emission Unabsorbed g-ray spectrum EBL-absorbed g-ray spectrum + cascade IC emission Several VHE (> 100 GeV) g-ray blazars are not detected by Fermi (100 MeV – 100 GeVg-rays)!

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