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

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

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

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.

Thomson Regime (γε 0 ≤1) Klein-Nishina Regime (γε 0 ≥1) Energy Dependence of Cooling Time Cooling time energy dependence  Electron Cooling regime  Seed photon energy

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

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

A Simulated Flare Within BLR Comparable decay timescales at different energy bands U BLR = 2.6 x ergs cm -3 ε 0 =3x10 -5 MT (Outside BLR) Decay timescale depends heavily on energy U MT = 2.6 x ergs cm -3 ε 0 =1.6x10 -7 Assumptions: L ext =10 44 ergs s -1 U EC /U B ~ 50, Γ=10

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

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

Practical Application Split flare into high energy (HE) and low energy (LE) bands Fit exponential to each peak Compare T F,LE and T F,HE Upper limit on 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

3C 454.3PKS PKS Desired sample: fast, bright flares Fast – observe electron cooling Bright – generate light curves in multiple energy bands Application to Fermi Data

Initial Results 3C (z=0.859) ΔT max = 6.2 hrs, R≤ 2.8 pc T f,HE =19.2±1.7 hr High Energy (E>500 MeV) T f,LE =19.6±2.1 hr Low Energy (E<500 MeV)

Initial Results ΔT max = 1.2 hrs, R≤ 4.2 pc T f,HE =2.11±0.55 hr High Energy (E>800MeV) T f,LE =1.54±0.38 hr Low Energy (E<800 MeV) PKS (z=0.432)

Initial Results PKS (z=0.361) T f,HE =10.92±3.3 hr High Energy (E>500 MeV) T f,LE =10.38±2.3 hr Low Energy (E<500 MeV) ΔT max = 4.5 hrs, R≤ 2.5 pc

PKS Flare A: T F,LE = /-6.7 h T F,HE = /-3.7 R<2.6 pc PKS Flare B: T F,LE = /-1.1 h T F,HE = /-1.0 R<1.1 pc

PKS Flare C: T F,LE = /-14.0 h T F,HE = /-6.0 R<7.7 pc PKS Flare D: T F,LE = /-3.6 h T F,HE = /-1.9 R < 1.5 pc

PKS Flare E: T F,LE = /-14 h T F,HE = /-0.11 R<27.1 pc PKS Flare F: T F,LE = /-1.6 h T F,HE = /-1.4 R<4.0 pc

Flare F Flare E Flare D Flare C Flare B Flare A

Flare F Flare E Flare D Flare C Flare B Flare A

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

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

Back-up Slides

Initial Results 3C (z=0.859) ΔT max = 6.2 hrs, R≤ 2.8 pc T f,HE =19.2±1.7 hr High Energy (E>500 MeV) T f,LE =19.6±2.1 hr Low Energy (E<500 MeV)

Initial Results ΔT max = 1.2 hrs, R≤ 4.2 pc T f,HE =2.11±0.55 hr High Energy (E>800MeV) T f,LE =1.54±0.38 hr Low Energy (E<800 MeV) PKS (z=0.432)

Initial Results PKS (z=0.361) T f,HE =10.92±3.3 hr High Energy (E>500 MeV) T f,LE =10.38±2.3 hr Low Energy (E<500 MeV) ΔT max = 4.5 hrs, R≤ 2.5 pc

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< ct var δ/(1+z) ~ cm Small size indicates that emission originates from far into the jet, R~10 17 cm (assuming the emitting region fills the jet cross section) Tavecchio 2010

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≤10 17 cm Poutannen & Stern 2010

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

What values of U and Γ are allowed?

Possibility of SSC? 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 R BLR scales R MT scales SSC not a concern.

Blazar SED Synchrotron Component Compton Component Image: PKS 1454 from Abdo 2010 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

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.

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

Brief Tour of Data Reduction Fermi Science Tools (fermi.gsfc.nasa.gov/ssc/) Event Data Data selection gtselect gtmktime Likelihood Analysis gtltcube gtexpmap makexml.py gtlike gtselect: select energy range, time span, ROI, etc 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

Numerical Simulation Spherical emitting region, Magnetic field (B), Electron injection q(γ,t) Electrons cool via synchrotron and IC cooling and escape t esc ≈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

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 (γε 0 ≤1) Ref: Rybicki & Lightman (1986), Jones (1968)

Fitting My fit: T R = 3.62 ± 0.64 h T F = 15.4 ± 1.6 h Published fit: T R = 4.5 ± 1 h T F = 15.0 ± 2 h Each component fit with exponential rise and decay:

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