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GAMMA-RAY BLAZARS NEAR EQUIPARTITION AND THE ORIGIN OF THE GEV SPECTRAL BREAK

Colliding Shell and External Shock Origin of the Prompt and Early Afterglow Emissions of Fermi GRBs Chuck Dermer Naval Research Laboratory, Washington, DC charles.dermer@nrl.navy.mil. Following ideas presented in papers with. Matteo Cerruti,* Catherine Boisson, Andreas Zech

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GAMMA-RAY BLAZARS NEAR EQUIPARTITION AND THE ORIGIN OF THE GEV SPECTRAL BREAK

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  1. Colliding Shell andExternal Shock Origin of the Prompt andEarly Afterglow Emissions ofFermi GRBs Chuck Dermer Naval Research Laboratory, Washington, DC charles.dermer@nrl.navy.mil Following ideas presented in papers with Matteo Cerruti,* Catherine Boisson, Andreas Zech LUTH, Observatoire de Paris, Meudon *Harvard-Smithsonian Center for Astrophysics & Benoît Lott CEN Bordeaux-Gradignan, Bordeaux, France GAMMA-RAY BLAZARS NEAR EQUIPARTITION AND THE ORIGIN OF THE GEV SPECTRAL BREAK IN 3C 454.3, Cerruti, et al., ApJL, submitted (2013) GAMMA-RAY BLAZARS NEAR EQUIPARTITION AND THE LOCATION OF THE GAMMA-RAY EMISSION SITE IN 3C 279, Dermer, et al., ApJ, submitted (2013) 7th Huntsville GRB Symposium Huntsville at Nashville 14-18 April 2013

  2. X-RAYS g-RAYS OPTICAL RADIO INTERNAL SHOCK EXTERNAL SHOCK Fireball/Blast Wave Model for GRBs >> 0.01 pc ~3×1016 (G/1000)2Dt(s) cm G2 G1 ISM Photosphere: R< 1012 cm Characteristic timescales: t90, tvar ~ (0.001 – 1) s Magnetically-dominated jets ICMART (Zhang and Yan 2011) Delayed onset Fermi-LAT g rays

  3. Blackbody/photospheric component in GRBs GRB 100724B GRB 090902B; Abdo et al. 2009, ApJ, 706, L138 Addition of blackbody component can improve spectral fits Possible solution to “Line of Death” Parameters of blackbody give nozzle radius (typically less than 1010 cm), and bulk Lorentz factor G; Pe’er et al. 2007, ApJ, 664, L1 Guiriec et al. 2011, ApJ, 727, L33

  4. Relativistic Bulk Motion in GRBs What is G, and why is it important? After redshift z, G is the most important property to make the extreme behavior of GRBs comprehensible Maximum collimation (and reduction from apparent to absolute powers) when jet opening angle For specific leptonic or hadronic models, we need to know z, G and B′ Crucial model discriminant, e.g., proton synchrotron model for GRB 080916C (Razzaque et al. 2010)

  5. How Gis determined (see Lü et al. 2012; Ghirlanda et al. 2012) • gg opacity method • 2. Afterglow onset method (optical or g-ray) • Early external forward emission method • Equipartition method (for determining G, B′, and R′b) Minimum bulk Lorentz factor: (Zou & Piran 2010) explained herein

  6. (Near-)Equipartition Modeling • Assume MeV (GeV) emission is nonthermal synchrotron • Use log-parabola function for electron distribution • Use observables and equipartition relations to derive G, B, gp,DR’b Have to subtract out photospheric emission Formalismvalid for colliding shells, external shocks, magnetic reconnection, jets in jets, etc. 3-parameter model: amplitude, curvature b, gp Observables of GRBs with known z: Lsyn tvar (tMTS or t90) Equipartition Relation: Spectral Relation: Exact in limit b→

  7. Solution to System of Equations What does equipartition mean? Minimum jet power Determined by SSC component Because of KN effects Equipartition between electron and total magnetic-field energy densities

  8. Application to GRB 110731A LGRB, z = 2.83, 10 keV – 10 GeV fluence ~4x10-5 erg/cm2 Tied for 5th in Eiso Ackermann, et al. 2013, ApJ, 763, 71

  9. GRB 110731A Ackermann, et al. 2013, ApJ, 763, 71 Timescales tGBM90 ~8 s tvar ~< 0.1 s tdly ~2.5 s tLAT90 ~20 s Derived quantities

  10. GRB 110731A Ackermann, et al. 2013, ApJ, 763, 71 es 1.4 2.1 5.1 3.3 Intervals log Ls* Gt01/8 = log(4pdL2×Fluence/Dt) a 53.22 4200 b 53.67 5350 c 53.82 6370 d 53.49 5240

  11. Fit to Epoch A data of GRB 110731A • zs = ze = tvar(s) = 1 • Nearly monoenergetic (blp> 8) electron distribution to fit Epoch A data • 0.1-100 GeV flux constrains log-parabola width blp> 0.5 of electron spectrum at other epochs • Low-energy Band a < -2/3 (natural asymmetry); require photospheric component if harder

  12. Constraints with varying zs • ze = 1, tvar = 1 s in explosion frame • 1 – 10 GeV UL at ~ 3×10-8 erg/cm s • Smaller G gives larger SSC g-ray flux • Increasing zs increases jet power, but power limitations depend on jet opening angle • zs < 1000 or would overproduce LAT emission • But tvar << 0.1 s

  13. Constraints with varying zs • ze = 1, tvar = 1 ms • Smaller tvar implies smaller emission region making same synchrotron power; therefore larger SSC g-ray flux • For tvar = 1 ms, zs < 10 or would overproduce LAT emission • G > 2750 if tvar = 1 ms • In equipartition (ze = 1)

  14. Bulk Lorentz Factors in GRBs (tvar in local frame) Ackermann et al. 2013 • For GRB 110731A, Epochs A and D (blp<1) • tvar = 1 s, G > 150 • tvar = 1 ms, G > 2700 • Obtain similar values of G using parameters of delayed LAT emission • 2 GeV g ray in Epoch D G > 600 • Eiso ~6-8×1053 erg • Why smaller values of deceleration G0 (<G)? Makes sense in the context of a colliding-wind/ external shock scenario

  15. Nonthermal Synchrotron GRB Modeling NG = Gqjet = 1 High- energy cutoff in CTA/HAWC range depends on tvar Model 1 4 tvar(s)1 10-3 G852 2021 B'(G) 13.7 1026 g'e 14300 1074 r'b(cm) 2.5e13 6.1e10 log[Pjet(erg/s)] 45.8 45.2 Calculate Model Emax(1020eV)/Z 1 0.9 4 0.4

  16. nFn Peaks in GRBs • Why do GRBs show a synchrotron Epk at ~50 keV – MeV energies, and a second emission-component/peak at ~GeV energies? • GRB detector sensitivity • Injection physics • In our model for the hard X-ray/soft g-ray emission of GRB 110731A, the principal electron Lorentz factor g’e,p ~ 3000 – 60,000 for tvar between 1 ms and 1 s, over allowed zs • In colliding shell model, g’e,p ~ h (mp/me) Grel ~ 2×104 (h /0.1)(Grel/10) • In external shock model, g’e,p ~ h (mp/me) G0 ~ 2×106(h /0.1)(G0/1000) Two-orders of magnitude difference in g’e,p gives 4 orders of magnitude difference in nonthermal synchrotron peaks, from ~100 keV to 1 GeV

  17. Summary • Nonthermal synchrotron paradigm • Applies to • Colliding shells • External shocks • Turbulence/reconnection • Jets within jets • Model inputs: • Synchrotron luminosity Ls • Synchrotron peak frequency Epk • Variability timescale tvar • New technique to derive Gfrom Swift/Fermi GBM/Fermi LAT data • Depends sensitively on tvar • Restrict range of zs from Fermi LAT observations • Perform equipartition spectral and temporal analysis on Fermi GBM/LAT GRBs to derive Gmin for different GRB pulses • Compare with other techniques: tgg, tdec, photosphere • 10-100 GeV regime crucial for searching for SSC component

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