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rays, cosmic rays and ν ’s s from from γ rays, cosmic rays and ν ’ γ Astrophysical Sources ( Sources (GRBs GRBs) ) Astrophysical Soebur Razzaque Soebur Razzaque U.S. Naval Research Laboratory, Washington, D.C. U.S. Naval Research Laboratory, Washington, D.C. National Research Council National Research Council CRIS 2010, September 13-17, CRIS 2010, September 13-17, Catania Catania, Italy , Italy

Fermi Gamma Ray Space Telescope Gamma Ray Space Telescope Fermi Large Area Telescope (LAT)  Pair conversion detector  Energy Range: 20 MeV to >300 GeV [20 MeV to 30 GeV for EGRET]  Effective Area: 9000 cm 2 [1500 cm 2 for EGRET]  Field of View: 2 sr [0.5 sr for EGRET]  Angular resolution: <3.5 o at >100 MeV [5.8 o at 100 MeV for EGRET] Gamma-ray Burst Monitor (GBM)  12 NaI detectors (8 keV - 1 MeV)  2 BGO detectors (150 keV - 30 MeV)  Field of view: 8 sr Survey mode (3.5 hr full sky) Pointing mode Automatic pointing mode for GRBs CRIS 2010, Catania Catania S. Razzaque S. Razzaque 2 CRIS 2010, 2

Sky Map of Fermi GRBs GRBs Sky Map of Fermi • 1 year from GBM turn on: 252 GRBs, 138 in the LAT FoV • 9 GRB detection at high energy by LAT in the first year CRIS 2010, Catania Catania S. Razzaque S. Razzaque 3 CRIS 2010, 3

Results from bright GRBs GRBs in Fermi LAT in Fermi LAT Results from bright  Observations: Observations:  Delayed onset of LAT ≥ 100 MeV MeV emission compared to emission compared to keV-MeV keV-MeV   Delayed onset of LAT ≥ 100 Hard additional power-law component Hard additional power-law component dominant in the dominant in the ≥ 100 MeV MeV  ≥ 100  and in some cases in the <100 and in some cases in the <100 keV keV ranges ranges  Extended Extended ≥ ≥ 100 100 MeV MeV emission in LAT well after emission in LAT well after keV-MeV keV-MeV emission emission  falls below GBM detection threshold falls below GBM detection threshold  Implications: Implications:   Jet velocity (bulk Jet velocity (bulk Lorentz Lorentz factor) factor)  Prompt emission (internal shocks?), afterglow emission Prompt emission (internal shocks?), afterglow emission   Emission mechanism: synchrotron, Compton, hadronic Emission mechanism: synchrotron, Compton, hadronic   Limits on quantum gravity models: Limits on quantum gravity models: M M QG ≥ 1.2 M M Pl [GRB 090510] [GRB 090510]  QG ≥ 1.2 Pl   Constraints on the extragalactic background light (EBL) models by Constraints on the extragalactic background light (EBL) models by  Stecker Stecker et al. (2006) [GRB 080916C, GRB 090902B] et al. (2006) [GRB 080916C, GRB 090902B] CRIS 2010, Catania Catania S. Razzaque S. Razzaque 4 CRIS 2010, 4

Delayed Onset of LAT Emission: GRB 080916C Delayed Onset of LAT Emission: GRB 080916C GRB 080916C GRB 080916C 8 – 250 keV Light Curves Light Curves GBM No significant emission No significant emission 0.26 – 5 MeV in the LAT energy in the LAT energy range for the first ~4 s ~4 s range for the first 1st >100 MeV MeV at ~4s at ~4s All LAT events 1st >100 1st >1 GeV at ~6s. 1st >1 GeV at ~6s. Delayed >100 MeV Delayed >100 MeV > 100 MeV LAT emission is common in emission is common in most other bright LAT most other bright LAT GRBs as well as well GRBs > 1 GeV Abdo et al. Science, 2009 CRIS 2010, Catania CRIS 2010, Catania S. Razzaque S. Razzaque 5 5

Delayed HE onset in other in other GRBs GRBs Delayed HE onset 090510 090902B 090926A CRIS 2010, Catania CRIS 2010, Catania S. Razzaque S. Razzaque 6 6

Hard Power Law Component in LAT (± ±GBM) GBM) Hard Power Law Component in LAT ( Time-integrated and time-resolved spectroscopy of 2 bright LAT GRBs GRBs Time-integrated and time-resolved spectroscopy of 2 bright LAT 090902B 090510 090902B 090510 Band α +2 β +2 Power-law  Phenomenological Band function (2 smoothly connected power laws, 4 parameters) fit ~100 keV - few MeV data well  Extra power-law component (2 parameters) is required to fit >100 MeV LAT emission and below ~100 keV in some cases CRIS 2010, Catania CRIS 2010, Catania S. Razzaque S. Razzaque 7 7

Extended HE Emission from LAT GRBs GRBs Extended HE Emission from LAT Bright LAT Bright LAT GRBs GRBs show significant show significant 090510 090510 high energy emission extending after high energy emission extending after the low energy emission low energy emission disappear disappear the t -1.38+/-0.07 below detectability detectability below 080916C 080916C CRIS 2010, Catania CRIS 2010, Catania S. Razzaque S. Razzaque 8 8

GRB Jet Velocity: bulk Lorentz Lorentz factor factor GRB Jet Velocity: bulk Very high jet bulk Lorentz Very high jet bulk Lorentz factor factor Minimum jet bulk Lorentz Lorentz factors factors Minimum jet bulk of bright Fermi LAT GRBs of bright Fermi LAT GRBs Calculated from γγ → e e + e - pair pair Calculated from γγ → + e - production opacity argument ( τ = 1) = 1) production opacity argument ( γγ τ γγ for ≥ ≥ 10 GeV source photons (co-spatial 10 GeV source photons (co-spatial for with keV-MeV keV-MeV photons) from photons) from GRBs GRBs with detected with Fermi LAT detected with Fermi LAT Some caveats Some caveats  The PL component may  The PL component may Originate from physically Originate from physically Separate region Separate region   Radiation transport effect Radiation transport effect Both lead to lower Γ by a factor ~2 Both lead to lower Γ by a factor ~2 Preliminary studies show that non- Preliminary studies show that non- Calculation of Calculation of Γ Γ from onset of from onset of LAT but bright GBM bursts has LAT but bright GBM bursts has afterglow also results in high values afterglow also results in high values systematically lower Γ systematically lower Γ CRIS 2010, Catania CRIS 2010, Catania S. Razzaque S. Razzaque 9 9

GRB Jet and Emission Model GRB Jet and Emission Model Rees, Meszaros, Piran and others … “standard GRB model” Synchrotron emission by shocked electrons for prompt and afterglow emission CRIS 2010, Catania CRIS 2010, Catania S. Razzaque S. Razzaque 10 10

Emission Mechanism in Fermi LAT Range Emission Mechanism in Fermi LAT Range Internal shocks Internal shocks   Synchrotron self Compton Synchrotron self Compton   ( (Abdo Abdo et al. 2010; et al. 2010; Toma Toma, Wu & , Wu & Meszaros Meszaros 2010) 2010)  Photopion Photopion and cascade radiation and cascade radiation  (Asano, (Asano, Guiriec Guiriec & & Meszaros Meszaros 2009) 2009) Proton synchrotron and cascade radiation Proton synchrotron and cascade radiation   (Razzaque, (Razzaque, Dermer Dermer & Finke 2010) & Finke 2010) External forward shock External forward shock   Synchrotron radiation from a highly radiative radiative blast wave blast wave  Synchrotron radiation from a highly  ( (Ghirlanda Ghirlanda et al. 2009; et al. 2009; Ghisellini Ghisellini et al. 2009) et al. 2009)  Synchrotron radiation from an adiabatic blast wave Synchrotron radiation from an adiabatic blast wave  (Kumar & (Kumar & Barniol-Duran Barniol-Duran 2009; 2009; Gao Gao et al. 2009) et al. 2009) Synchrotron radiation from two component jet  Synchrotron radiation from two component jet  ( (Corsi Corsi, , Guetta Guetta & & Piro Piro 2009) 2009)  Proton synchrotron radiation Proton synchrotron radiation from an adiabatic blast wave from an adiabatic blast wave  (Razzaque 2010) (Razzaque 2010) CRIS 2010, Catania Catania S. Razzaque S. Razzaque 11 CRIS 2010, 11

Synchrotron Self Compton: GRB 090510 Synchrotron Self Compton: GRB 090510 ApJ, 2010) , 2010) et al., ApJ Abdo et al., (Abdo (  Can not produce delay longer than Can not produce delay longer than  the pulse width, the pulse width, ~ 0.01 s - 0.1 s ~ 0.01 s - 0.1 s Can not produce excess emission Can not produce excess emission   at <100 at <100 keV keV  Energetically efficient Energetically efficient  CRIS 2010, Catania Catania S. Razzaque S. Razzaque 12 CRIS 2010, 12