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Determining the location of the GeV emitting zone in fast, bright blazars

Determining the location of the GeV emitting zone in fast, bright blazars. Amanda Dotson, UMBC Markos Georganopoulos (advisor), UMBC/GSFC Eileen Meyer, STScI Kevin McCann, UMBC. AAS Meeting, Washington DC January 2014. The Issue At Hand.

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Determining the location of the GeV emitting zone in fast, bright blazars

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  1. Determining the location of the GeV emitting zone in fast, bright blazars Amanda Dotson, UMBC MarkosGeorganopoulos (advisor), UMBC/GSFC Eileen Meyer, STScI Kevin McCann, UMBC AAS Meeting, Washington DC January 2014

  2. The Issue At Hand Where is the gamma-ray emission zone (GEZ) in blazars? ? Molecular Torus (pc scale) ? Broad Line Region (sub-pc scale) Jet Not to scale!

  3. Locating the GEZ with Flare Decay Times Unknown: GEZ Location ??? Observable: Fast gamma ray flares

  4. Locating the GEZ with Flare Decay Times GEZ Location Critical difference between GEZ in BLR vs MT energy of the seed photons. Seed photon energy ε0,MT= 10-7 (~.1 eV) ε0,BLR = 10-5 (~10 eV) Electron cooling time energy dependence Thomson Regime (γε0 ≤1) Klein-Nishina Regime (γε0≥1) Observable: Flare decay time energy dependence Published in ApJL Dotson, et al. 2012

  5. Locating the GEZ with Flare Decay Times MT BLR Cooling time nearly flat (energy independent) Cooling time energy dependent Dotson, et al. 2012 Falling time  Electron cooling Seed Photons  Photon origin

  6. Application to Fermi Data • Fit exponential rise/decay to each peak: • Split data into high energy (HE) and low energy (LE) bands of ≈TS PKS 1510 Unused Flare PKS 1510 “Good” Flare

  7. Application to Fermi Data • Fit multiple models • Choose best fit using Bayesian information criterion (BIC L: Likelihood k: # model parameters n: # data points PKS 1510-089 1 peak model BIC = 0.863 BIC = 0.545 2 peak model BIC = 5.91 BIC = 5.61

  8. An Interesting Flaring State of PKS 1510-089 • Optical EVPA rotated by ~720° over the course of 5-day flaring period (6 flares total) • % Optical polarization and R-band spike during γ-ray flaring period • Later detection of new superluminal knot ejected from radio core • Interpretation (from Marscher 2010): flaring state caused by knot travelling down spiral magnetic field and passing through a shock at pc-scale Plots from Marscher 2010

  9. An Interesting Flaring State of PKS 1510-089 • Optical EVPA rotated by ~720° over the course of 5-day flaring period (6 flares total) • % Optical polarization and R-band spike during γ-ray flaring period • Later detection of new superluminal knot ejected from radio core • Interpretation (from Marscher 2010): flaring state caused by knot travelling down spiral magnetic field and passing through a shock at pc scale Image from Marscher 2010 Plots from Marscher 2010

  10. Application to PKS 1510 Interesting Flares: Flare 5  LE (E<500 MeV)  HE (E>500 MeV) Flux (ph s-1 cm-2)

  11. Application to PKS 1510 Interesting Flares: Flare 7  LE (E<500 MeV)  HE (E>500 MeV) Flux (ph s-1 cm-2)

  12. Application to PKS 1510 Interesting Flares: Flare 7  LE (E<500 MeV)  HE (E>500 MeV) Flux (ph s-1 cm-2)

  13. An unusual case: Flare 8  LE (E<500 MeV)  HE (E>500 MeV) Flux (ph s-1 cm-2) • Very fast falling times (<3h) • Fit unsuccessful • LE flare seems to fall faster than HE flare

  14. Summary & Conclusions • Summary • Theory predicts flare decay time energy dependence GeV photon origin (Dotson et al. 2012) • Distinct falling times of flares 5, 7 (and 8?) indicate MT location of GeV emission zone • In agreement with Conclusions This method has been successful in locating the GeV photon origin in 5 of the brightest flares of Fermiblazars within a few pc of the central black hole.

  15. Back-up Slides

  16. Dominant Source of Seed Photons Assumptions: Ldisk = 1045 ergs s-1 , Lext=0.1Ldisk,Lsynch=1046 ergs s-1 RBLR = 1017 cm, RMT = 1018 cm, Rblob=1016 cm Γbulk=10

  17. Cooling Differences • BLR • U’=2.6 ergs cm-3 • Dominated by emission lines • ε0 = 10-5 (~10 eV) • R = 1017 cm • MT • U’=2.6 ×10-2 ergs cm-3 • BB emission, peaking at T~1000 K • ε0 = 10-7 (~.1 eV) • R = 1018-19 cm The critical difference between the BLR and the MT is the energy of the seed photons.

  18. What values of U and Γ are allowed?

  19. Thomson vs KN Regime Thomson cross section (purely classical): γε0 ≤1 Klein-Nishina cross section (derived through QED): γε0 ≥1 Scattering in the KN regime is much less efficient than scattering in the Thomson regime

  20. Will light-travel effects erase cooling differences? Short answer: No.

  21. Application to Fermi Data Upper limit on region of photon emission (RGeV)

  22. Fitting • Each component fit with exponential rise and decay: • Fit different models (change # peaks, flat/sloped background,etc) • Choose best fit model using BIC and AIC L: Likelihood k: # model parameters n: # data points

  23. Future Work • How does SSC model compare with these results? • What is the energy dependence of Tfin the case of SSC? • Is there a similar way of constraining RGeV for SSC seed photons?

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