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

1. Determining the location of the GeV emitting zone in fast, bright blazars Amanda Dotson, UMBC MarkosGeorganopoulous, UMBC/GSFC Eileen Meyer, STScI MARLAM Sept 27, 2013

2. The Issue At Hand Where is the site of the GeV emission in blazars?

3. The Issue At Hand Where is the site of the GeV emission in blazars? ? Molecular Torus (pc scale) ? Broad Line Region (sub-pc scale) Jet Not to scale!

4. 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

5. 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.

6. Energy Dependence of Cooling Time Thomson Regime (γε0 ≤1) Klein-Nishina Regime (γε0≥1) Cooling time energy dependence  Electron Cooling regime  Seed photon energy

7. Cooling time nearly flat (energy independent) BLR Cooling time energy dependent MT Energy dependence of cooling time Seed Photons Location

8. Observable: Decay time energy dependence Electron Cooling regime Seed photon energy GEZ Location

9. A Simulated Flare • Within BLR • Comparable decay timescales at different energy bands • UBLR = 2.6 x 10-2 ergs cm-3 • ε0=3x10-5 • MT (Outside BLR) • Decay timescale depends heavily on energy • UMT= 2.6 x 10-4 ergs cm-3 • ε0=1.6x10-7 Assumptions: Lext=1044 ergs s-1 UEC/UB ~ 50, Γ=10

10. MT BLR Δt ~ 8 hours Δt ~ 2 hours Energy dependence of decay time Location of GEZ

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

12. Practical Application • Split flare into high energy (HE) and low energy (LE) bands • Fit exponential to each peak • Compare TF,LE and TF,HE • Upper limit on RGeV

13. 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

14. Application to Fermi Data Desired sample: fast, bright flares Fast – observe electron cooling Bright – generate light curves in multiple energy bands 3C 454.3 PKS 1510-089 PKS 1222+216

15. Initial Results Low Energy (E<500 MeV) High Energy (E>500 MeV) 3C 454.3 (z=0.859) Tf,LE=19.6±2.1 hr Tf,HE=19.2±1.7 hr ΔTmax= 6.2 hrs, R≤ 2.8 pc

16. Initial Results PKS 1222+216 (z=0.432) Low Energy (E<800 MeV) High Energy (E>800MeV) Tf,LE=1.54±0.38 hr Tf,HE=2.11±0.55 hr ΔTmax= 1.2 hrs, R≤ 4.2 pc

17. Initial Results PKS 1510-089 (z=0.361) High Energy (E>500 MeV) Tf,HE=10.92±3.3 hr Low Energy (E<500 MeV) Tf,LE=10.38±2.3 hr ΔTmax= 4.5 hrs, R≤ 2.5 pc

18. PKS 1510-089 Flare A: TF,LE=10.1 +4.8/-6.7 h TF,HE= 7.35 + 3.1/-3.7 R<2.6 pc PKS 1510-089 Flare B: TF,LE=2.89 +0.82/-1.1 h TF,HE= 3.69 + 0.69/-1.0 R<1.1 pc

19. PKS 1510-089 Flare C: TF,LE=37.6 +13.0/-14.0 h TF,HE= 11.1 + 3.9/-6.0 R<7.7 pc PKS 1510-089 Flare D: TF,LE=4.15 +1.6/-3.6 h TF,HE= 2.57 + 1.3/-1.9 R < 1.5 pc

20. PKS 1222+216 Flare E: TF,LE=40.9 +12/-14 h TF,HE= 0.149 + 0.78/-0.11 R<27.1 pc PKS 1222+216 Flare F: TF,LE=2.11 +1.9/-1.6 h TF,HE= 1.46 + 0.91/-1.4 R<4.0 pc

21. Flare F Flare E Flare D Flare C Flare B Flare A

22. Flare F Flare E Flare D Flare C Flare B Flare A

23. Future Work • Apply diagnostic to other bright flares in a larger sample • Needed: fast, bright flares • Search for patterns (or lack thereof) of energy dependence in larger sample of flares • Perform analysis without any kind of binning, on a photon-by-photon basis

24. Summary/Conclusions • Powerful blazars undergo bright, fast GeV flares • Energy dependence of decay time of flares can reveal the source of seed photons • Source of seed photons indicates location of flaring region • Possible to detect cooling differences at 95% confidence interval

25. Back-up Slides

26. Initial Results Low Energy (E<500 MeV) High Energy (E>500 MeV) 3C 454.3 (z=0.859) Tf,LE=19.6±2.1 hr Tf,HE=19.2±1.7 hr ΔTmax= 6.2 hrs, R≤ 2.8 pc

27. Initial Results PKS 1222+216 (z=0.432) Low Energy (E<800 MeV) High Energy (E>800MeV) Tf,LE=1.54±0.38 hr Tf,HE=2.11±0.55 hr ΔTmax= 1.2 hrs, R≤ 4.2 pc

28. Initial Results PKS 1510-089 (z=0.361) High Energy (E>500 MeV) Tf,HE=10.92±3.3 hr Low Energy (E<500 MeV) Tf,LE=10.38±2.3 hr ΔTmax= 4.5 hrs, R≤ 2.5 pc

29. Variability Arguments • Short variability has been observed with Fermi with timescales ~3 hours in the GeV range (Tavecchio 2010) • Variability timescale constrains size of emission region • r< ctvarδ/(1+z) ~ 1015 cm • Small size indicates that emission originates from far into the jet, R~1017 cm (assuming the emitting region fills the jet cross section) Tavecchio 2010

30. Explaining the Fermi GeV Breaks • GeV emission of bright blazars better modeled with a broken power law • Break at about ~2 GeV can be explained by pair absorption of He II Lyα line and continuum (Poutannen & Stern 2010) • He II line produced closer to BH • As a result, emitting region should be at R≤1017 cm Poutannen & Stern 2010

31. Relations Between Radio and Υ-rays • Two mm flares associated with jet component ~14 pc from BH • γ-ray maximum coincides temporally with optical flare and polarization maximum located at ~14 pc from the BH • γ-ray emission cospatial with radio core, located ~14 pc from black hole OJ 287

32. What values of U and Γ are allowed?

33. Possibility of SSC? SSC not a concern. RBLR scales RMT scales 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

34. Blazar SED • Leptonic Model: • Electron/positron population in the jet results in observed emissions • Synchrotron Radiation • (Sub-mm to x-ray) • Inverse Compton Scattering • (MeV to TeV) • Same population of electrons for both synchrotron and IC Compton Component Synchrotron Component Image: PKS 1454 from Abdo 2010

35. Relativistic Effects Depending on the direction the photons enter the jet, U’ (co-moving energy density) scales as different factors of Γ (Dermer 1994) For isotropic photon field: For photons entering from behind: This determines which photon field is prevalent at different distances from the BH.

36. 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

37. Brief Tour of Data Reduction Fermi Science Tools (fermi.gsfc.nasa.gov/ssc/) gtselect: select energy range, time span, ROI, etc Data selection gtselect gtmktime Likelihood Analysis gtltcube gtexpmap makexml.py gtlike Event Data gtmktime: creates good time intervals based on spacecraft data file gtltcube: calculates livetime as a function of sky position and off-axis angle gtexpmap: calculates exposure map for ROI makexml.py: makes a model file for all sources in ROI (including galactic and eg backgrounds) gtlike: performs likelihood analysis of LAT data To make a light curve, loop over these steps for each time bin

38. Numerical Simulation • Spherical emitting region, Magnetic field (B), Electron injection q(γ,t) • Electrons cool via synchrotron and IC cooling and escape tesc≈R/c • Evolution of electron energy distribution (EED) described by • Reaches steady state, outputs synchrotron, SSC, EC luminosities • To simulate a flare, the electron injection increased for a fixed time

39. Radiative Processes • Synchrotron Radiation • Results from relativistic particles accelerated by a magnetic field B • Relativistic cyclotron radiation • Inverse Compton Scattering • High-energy electron interacts with low-energy photon, upscatters the photon Thomson regime (γε0 ≤1) Ref: Rybicki & Lightman (1986), Jones (1968)

40. Fitting Each component fit with exponential rise and decay: My fit: TR = 3.62 ± 0.64 h TF = 15.4 ± 1.6 h Published fit: TR = 4.5 ± 1 h TF = 15.0 ± 2 h

41. Application to Fermi Data • Fermi Overview • LAT (Large Area Telescope) • • 20 MeV300 GeV • • 2.4 srFoV (scans entire sky every ~3hrs) • Angular resolution < 3.5° (100 MeV)