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Simulations of Thermal GRBs as observed by GLAST GBM+LAT

Simulations of Thermal GRBs as observed by GLAST GBM+LAT. Milan Battelino Stockholm Observatory DC2 Closeout Meeting 31 May - 2 June 2006. Outline. Background The Hybrid Model Simulation flow Results. a. b. GRB Standard Model. Band, D. et al.:1993 ApJ 413 , 281.

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Simulations of Thermal GRBs as observed by GLAST GBM+LAT

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  1. Simulations of Thermal GRBs as observed by GLAST GBM+LAT Milan Battelino Stockholm Observatory DC2 Closeout Meeting 31 May - 2 June 2006

  2. Outline • Background • The Hybrid Model • Simulation flow • Results

  3. a b GRB Standard Model Band, D. et al.:1993 ApJ413, 281 Excellent fit for majority of GRB spectra in BATSE energy window a, b, Ec , Aband

  4. Fermi-shock-accelerated e– distribution: p ~ 2.2 Ne g-p Observed region BATSE logg Low energies Self absorption High energies Cut off Characteristic synchrotron frequency Cooling frequency Optically Thin Synchrotron Spectrum FC: s = -1.5 s = -2/3 s = -2.1 SC: s = -1.6

  5. Time-resolved spectra from 57 bright BATSE bursts A substantial fraction of the time-resolved spectra from bright BATSE bursts show hard sub-peak spectra! -2/3 Line of Death Crider et al: 1997, ApJ479, L39+ Preece et al: 1998, ApJ506, L23 Hard to explain with optically thin synchrotron model! This has to be considered when implementing a model. Also high energy components in the MeV – GeV band...

  6. Other Models...Review paper by GRB Group, 2006 • Synchrotron and Inverse Compton • Electron IC Scattering • Synchrotron Self-Compton • Proton Synchrotron Emission • Thermal Components + Synchrotron • Pion production and cascades • Hadronic Cascades • Neutron-proton decoupling

  7. Bose-Einstein function + Powerlaw(s) GRB 911016 Hybrid Model Ryde, F: 2004, ApJ614, 827 m = 0 : Planck spectrum : a = 1 m >> 0 : Wien spectrum : a = 2 Blackbody + Powerlaw kT, AkT, s, Apow

  8. -2/3 -1.6 ...also: a peak at s = -1.6, close to s = -1.5 LOD not a problem in Hybrid Model LOD not a problem with

  9. How to simulate Hybrid Model? • Model independent simulator software (C++) producing photon histogram files • Extend gtobssim software (C++): • New celestialSource class: GRBtemplateManager (by Nicola Omodei) that reads photon histogram files • Extend GBM Tools package (IDL): • Read photon histogram files

  10. N(E,t) Model PlotDevice 1 C(E,t) 1..n Component 1 1 P(t) ComponentList Parameter 1..n Blackbody Powerlaw 1 Hybrid ParameterList Lightcurve Breakpoint Simple Burst Modeler

  11. Hybrid Model Parameters Blackbody Component • Lightcurve (Flux) • Temperature (kT) • Normalization Powerlaw Component • Lightcurve (Flux) • Spectral index/indices • Breakpoints • Normalization

  12. BATSE window High energy cut-off Competition between the acceleration (heating) of the electrons and the radiative cooling leads to a maximal energy that the electrons can be accelerated to. Blackbody component Broken power-law : synchrotron emission spectrum Hybrid Model Simulation GRB 911016 ~ 3 GeV based on results by de Jager et al, 1996, ApJ457, 253

  13. File Header GRBtemplateManagerNicola Omodei • Photon Histogram: • Number of energy bins (columns): • Min Energy: • Max Energy: • Number of time bins (rows): • Timebinwidth: • Energy binning:

  14. GBM Tools extensions • GRBtemplate photon histogram file • populate energy bins from LAT photon histogram file with internal energy binning defined by energy grid • Energy grid photon histogram file • GBM Simulator reads definition file, determines energy grids for NaI and BGO detectors and saves energy grids as files • SBM reads energy grid files and produces histogram files • GBM Simulator reads SBM histogram files to produce, apportion photons and create TTE files.

  15. BATSE Trigger Data GLAST Definition file XSPEC GBM Simulator 1 5 Model Parameter Values + guesses NaI/BGO Energy Grid SBM 2 6 LAT lightcurve histogram file Separate NaI and BGO lightcurve histogram files gtobssim gtselect gtrspgen 3 GBM Simulator 7 LAT FITS and response files NaI/BGO TTE, background and response files gtbin 4 8 XSPEC 9 Simulation Flow

  16. q = 27.1o, f = 95.3o NaI #2 + NaI #9 + BGO #1 + LAT XSPEC Model Resolution : 1 x 5.0 s Blackbody + (Broken Powerlaw x High Energy Cutoff) s1 = -1.30 +/- 0.04 Resolution : 5 x 1.0 s c2n= 0.9 s1 = -1.33 +/- 0.02 s2 = -1.71 +/- 0.02 s2 = -1.81 +/- 0.08 Joint Spectral AnalysisGRB 911016 XSPEC Result SBM input s1 = -1.3 s2 = -1.7

  17. XSPEC Result SBM Input = 0.78 S1 = -1.6 S1 = -1.7 +/- 0.03 S2 = -2.1 S2 = -2.1 +/- 0.2 GRB 941026 Time integrated: 0.0 - 5.0 s q = 27.1o, f = 95.3o NaI #2 + NaI #9 + BGO #1 + LAT

  18. Conclusion • Hard to determine high energy cutoff in time-resolved spectra above 3 GeV • Blackbody component easily detected if it is the cause of spectral hardness • Position of powerlaw breakpoint hard to determine when strong blackbody component

  19. The End Thanks to: Nicola Omodei, Valerie Connaughton and Felix Ryde

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