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High Energy Emissions from Gamma-ray Bursts (GRBs)
Soeb Razzaque Penn State University TeV 06
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Bright flash of -rays outshining the entire universe for seconds
Gamma Ray Burst Most violent explosion in the Universe! Bright flash of -rays outshining the entire universe for seconds Total energy output in -rays ~ erg Credit: Tyce DeYoung Peak photon energy ~0.1-1 MeV Non-thermal -ray spectrum Isotropic distribution Rate ~1000/year Extra-galactic (redshift~1-2) TeV 06
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GRB Prompt Emission Highly variable -ray emission
(down to milliseconds) Compact source Long bursts Short bursts Time (s) Bi-modal distribution of burst duration Different origins TeV 06
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GRB Afterglow BeppoSAX
Late time (hours-days) emission of X-ray, UV, optical light BeppoSAX Feb GRB Mar2 Identify host galaxy redshift TeV 06
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Core collapse Binary mergers X ISM UV O Afterglow Isotropic-equivalent
total energy outflow GRB Relativistic jetted outflow Initial fireball radius Accretion disk Initial temperature Binary mergers TeV 06
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Gamma-ray Spectrum Time-averaged spectrum fitted by
broken power-laws (Band fit) Non-thermal Break energy ~0.1-1 MeV Origin: Internal shocks e-synchrotron radiation (low energy) Inverse Compton scattering (high energy) Observation: Theoretical model: e - shock acceleration =2 for strong shock Synch/IC spectrum Fast cooling: shock accelerated e - population lose energy completely (e to ) within dynamic time ~0.1 model parameter TeV 06
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Afterglow Spectrum Ambient medium Reverse | Forward shocks
e -synchrotron cooling time longer than dynamic time Reverse | Forward shocks Break frequency decreases in time at rate depending on constant (ISM) or wind (density r -2 ) ambient medium Sari, Piran & Narayan ’98 TeV 06
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TeV -ray Detection Status
Milagro Milagrito: GRB a Tentative 3 detection Unknown redshift (less than 100 Mpc?) Atkins et al. ‘00 Tibet Array: 50-60 GRB stacked in time coincidence with MeV 6 significance Amenomori et al. ‘96 GRAND: GRB Reported significance 2.7 Poirier et al. ’03 MAGIC: GRB050713a Flux upper limits Albert et al. ‘06 Tibet Array GRAND Array MAGIC TeV 06
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GeV -ray Detection GLAST Future detector GRB 970217 GRB 941017
Hurley et al. ‘94 GRB GRB t<14 s t <47 s t < 80 s Handful of GRB detection at ~GeV by EGRET Hard spectra and delayed emission More energy in HE component? Need more data! GLAST t < 113 s Future detector t < 211 s TeV 06 Gonzalez et al. ‘03
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High Energy -rays from GRBs
Electromagnetic process: Inverse Compton (IC) Maximum electron energy ~100 TeV Maximum -ray energy ~TeV Inefficient in the Klein-Nishina limit Hadronic Process: Photomeson 0 decay Maximum proton energy ~1020 eV Maximum -ray energy ~EeV In general inefficient: opacity~1 (long) <1 (short) Single or multi (internal-external shocks) zone(s) emission? High energy -rays may attenuate at the source -rays with energy >100 GeV are attenuated in background radiation fields (IR/CMB) TeV 06
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Which Model? One zone model for MeV and HE
Time delay by slower p cascade and secondary radiation Early Afterglow: >100 MeV IC e-sync Boettcher & Dermer ‘98 p-sync tdec ~2 Internal shock MeV -rays External shock high energy Insignificant proton contribution Zhang & Meszaros ’01 Granot & Guetta ‘03 TeV 06
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-ray Opacity of the Universe
>100 GeV -rays from GRBs suffer attenuation in IR & CMB background e Coppi & Aharonian ‘97 High energy -ray attenuation from GRBs may probe astrophysical model(s) Baring ‘99 TeV 06
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HE Photon Opacity in GRBs
Optical depth Internal shock radius Razzaque, Meszaros & Zhang ‘04 TeV 06
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GRB Prompt and Delayed Spectra
Re-processed high energy -ray 10-17 G IG B-field 10-20 G Razzaque, Meszaros & Zhang ‘04 TeV 06
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Diffuse <TeV -rays from GRBs
Casanova, Dingus & Zhang ‘06 TeV 06
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>TeV -ray from UHE Cosmic-ray
Shock-acceleration in GRB ≥1020 eV cosmic-rays >1 TeV -ray fluence 1051 erg GRB energy at 100 Mpc Cascades on IR/CMB background radiation Delayed emission ~day Patchy IGM (80% voids w. B10-15 G, 20% w. B~10-11 G) TeV Fluence ~2% of energy in GZK protons Waxman & Coppi ’96 Dermer ’02 Armengaud, Sigl & Miniati ‘06 TeV 06
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GRB Fireball Evolution
Initial fireball Coulomb Compton nuclear Baryon loading coasting fireball Initial fireball Inelastic p-n scattering n-p decouples TeV 06 Derishev, Kocharovsky & Kocharovsky ‘99
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n-p Decoupling in Short GRB
Radius Rnp~RTh Razzaque & Meszaros ‘06 TeV 06
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n-p Decoupling Gamma-rays
Only photons produced at photosphere may escape un-attenuated Bahcall & Meszaros ‘00 (LGRB) 0 decay photon energy (SGRB) Razzaque & Meszaros ‘06 Probability Flux from an SGRB at z=0.1 MILAGRO GLAST : Too small effective area MILAGRO Energy below threshold? TeV 06
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Short GRB Model Flux Predictions
Model parameters GRB Distance (z) L_iso (erg/s) Duration (s) E (GeV) Flux (/cm2/s) 040924 050509b 051103 051221 0.859 0.225 0.001(?) 0.547 1.48E52 8.6E48 2.6E47 1.7E51 0.6 0.128 0.17 1.4 22 59 36 9.7E-6 2.3E-7 8.6E-4 2.3E-6 Data credits: Pablo Saz Parkinson Predictions These are still below detection Need bigger detectors with lower threshold TeV 06
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GeV Gamma-rays from Short GRB
IC scattering Razzaque & Meszaros ‘06 TeV 06
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Late X-ray Flares in GRB
Various models: Refreshed shocks IC from reverse shock External density bumps Multiple component jet Late central engine activity Main constraints: sharp rise and decline GeV-TeV rays: IC scattering of x-ray photons by external forward shocked electron GRB X-ray flare Underlying afterglow light curve t -0.8 Burrows et al. ’05, Zhang et al. ‘05 Wang, Li & Meszaros ‘06 TeV 06
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HE from Old GRB Remnants
HESS J Age: 1.5×104 yr ; Distance: 12 kpc 0 decay model ≤10’ 10’≤≤25’ 25’≤≤1o Atoyan, Buckley & Krawczynski ‘06 TeV 06
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HE from Old GRB Remnants
GRB jet: p +n neutron decay: n e - e - CMB e - HE W49B TeV Ioka, Kobayashi & Meszaros ‘04 TeV 06
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Conclusion GRBs are the brightest MeV -ray transient sources in the universe GeV and TeV (tentative) -rays have been observed from a few bursts Both Leptonic and Hadronic models may account for GeV data Need more data! Short GRBs may produce ~100 GeV -rays Less luminous than long GRBs but much nearer Less attenuation in background radiation TeV detection in current detectors requires luminous and nearby GRBs Need more GeV-TeV data need bigger detector! TeV 06
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