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

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

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

Locating the GEZ with Flare Decay Times Thomson Regime (γε 0 ≤1) Klein-Nishina Regime (γε 0 ≥1) ε 0,MT = (~.1 eV) ε 0,BLR = (~10 eV) Critical difference between GEZ in BLR vs MT  energy of the seed photons. Seed photon energy GEZ Location Electron cooling time energy dependence Observable: Flare decay time energy dependence Published in ApJL Dotson, et al. 2012

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

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

Application to Fermi Data Fit multiple models Choose best fit using Bayesian information criterion (BIC L: Likelihood k: # model parameters n: # data points 1 peak model BIC = BIC = peak model BIC = 5.91 BIC = 5.61 PKS

An Interesting Flaring State of PKS Plots from Marscher 2010 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

An Interesting Flaring State of PKS Plots from Marscher 2010 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

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

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

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

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

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 Fermi blazars within a few pc of the central black hole.

Back-up Slides

Inside BLROutside BLR Accretion Disk Photons U’ AD ~ ergs cm -3 BLR Photons U’ BLR ~ 1.0 ergs cm -3 U’ BLR ~ ergs cm -3 MT Photons U’ MT ~ ergs cm -3 Dominant Source of Seed Photons Assumptions: L disk = ergs s -1, L ext =0.1L disk,L synch =10 46 ergs s -1 R BLR = cm, R MT = cm, R blob =10 16 cm Γ bulk =10

BLR U’=2.6 ergs cm -3 Dominated by emission lines ε 0 = (~10 eV) R = cm Cooling Differences MT U’=2.6 ×10 -2 ergs cm -3 BB emission, peaking at T~1000 K ε 0 = (~.1 eV) R = cm The critical difference between the BLR and the MT is the energy of the seed photons.

What values of U and Γ are allowed?

Thomson vs KN Regime Thomson cross section (purely classical): γε 0 ≤1 Klein-Nishina cross section (derived through QED):γε 0 ≥1 Scattering in the KN regime is much less efficient than scattering in the Thomson regime

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

Application to Fermi Data Upper limit on region of photon emission (R GeV )

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

Future Work How does SSC model compare with these results? What is the energy dependence of T f in the case of SSC? Is there a similar way of constraining R GeV for SSC seed photons?