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Alessandra Galli 1,2,3

GeV emission from Gamma-Ray Bursts. Alessandra Galli 1,2,3. 1 : INFN-Trieste, 2 : University of Rome “La Sapienza” 3 : INAF/IASF-Rome. Asi Science Data Center 3 July 2007. Very High Energy emission. Hurley et al. 1994.

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Alessandra Galli 1,2,3

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  1. GeV emission from Gamma-Ray Bursts Alessandra Galli1,2,3 1: INFN-Trieste, 2:University of Rome “La Sapienza” 3: INAF/IASF-Rome Asi Science Data Center 3 July 2007

  2. Very High Energy emission Hurley et al. 1994 At high energies additional emission process is required, such as Inverse Compton A. Galli-ASDC, 3 July 2007

  3. Galli & Piro 2007 External Shock: Inverse Compton vs Synchrotron Y=LIC/Lsyn FAST COOLING: =1, Y∝(εe/εB)1/2 SLOW COOLING: <1, Y∝(εe/εB)1/2 εB=8·10-2 (E53 n)-1/4 [1+(εe/εB)1/2]-1/2 · ·(εe/εB) -1/2 Td1/4 (1+z)-1/4 Relative importance of IC and synchrotron emission greater in fast cooling than in slow cooling The importance of IC increases with E53 and n A. Galli-ASDC, 3 July 2007

  4. Detectability of the Inverse Compton component in the GeV band with LAT GLAST Galli & Piro 2007 Tint=104 sec Fth(1GeV)~10-10 erg cm-2s-1 Tint=500 sec Fth(1GeV)~2·10-9 erg cm-2s-1 A. Galli-ASDC, 3 July 2007

  5. IC Spectra 50 ksec 500 sec 10 ksec Γ0=120, E53 = 1.0, n = 5, εe= 0.2, p=2.5, and z=1. Green, blue and red spectra are obtained respectively for εB= 10-4, εB= 10-3, and εB= 10-2. A. Galli-ASDC, 3 July 2007

  6. IC emission from afterglow: application to GRB 940217 High energy emission, 30 MeV-30 GeV, up to 5000 sec (Hurley et al. 1994) best fit power law: γ=2.830.64  S~7·10-6 erg cm-2 , F ~2·10-9 erg cm-2 s-1 E53 = 5.0, n = 3.0, εe=0.07, εB= 0.001, p = 2.5, z =1 500 sec 5000 sec F ~t1/3 v < νc,IC F ~t1/8 νc,IC < v < νi,IC F~t-(10-9p)/8νi,IC < ν νc,IC < νi,IC < νobsγ=(p+2)/2 p=2.5  γ=2.25 A. Galli-ASDC, 3 July 2007

  7. Delayed External Shock scenario: thick shell fireballs as a possible explanation for X-ray flares Δ=cteng, thus teng >tdec. Most of the energy is transferred to the surrounding material around the end of the engine activity. Afterglow decay described by a power law only if the time is measured from the instant of the central engine turns off (Lazzati & Begelman, 2005). The flare is produced by an external shock caused by an energy injection lasting until the time of the flare occurrence, i.e. requires long lasting central engine activity A. Galli-ASDC, 3 July 2007

  8. GeV flares in association with X-ray flares -Internal Shock: Low Lorentz factor, low Thompson cross section  no bright GeV flares Different emitting regions  temporal dilatation -External Shock: Higher Lorentz factor  brighter high energy flares Same region and electrons population  similar temporal profiles External Shock Internal Shock 2: IC + 2nd order IC Internal Shock 1: Synchr + self IC A. Galli-ASDC, 3 July 2007

  9. IC emission from a thick shell fireball ISM-Fast Cooling 100 GeV 1 GeV 1 GeV 100 GeV X-ray Galli & Piro, 2007 niIC niIC niIC E53=5,=300, n=1, e=0.1,B=10-4, p=2.5, z=1, t0=500 s A. Galli-ASDC, 3 July 2007

  10. Conclusion • GLAST LAT – and for nearest bursts also AGILE, will be able to detect IC emission from the afterglow of Gamma-Ray Bursts; • Both in the framework of the internal shocks scenario and in that of the external shocks late X-ray flares are related to a long lasting central engine activity; • X-ray flares can be attended by GeV flares produced by IC, that could be detected by GLAST; • IC emission from afterglow can explain also the delayed high energy emission detected by EGRET in GRB 940217; • We expect similar temporal profiles for X-ray and high energy flares in the context of External Shock.

  11. Bonus Slide

  12. GeV flares in association with X-ray flares X-ray flares overlap with the afterglow emission, thus X-ray flares photons can be Inverse Compton scattered in the GeV-TeV band by afterglow electrons. • Late Internal Shock model • Two possible mechanisms (Wang et al. 2006, Fan & Piran 2006): • X-ray flares  synchrotron GeV flares  self IC emission • X-ray flares  IC emission GeV flares  2° order IC on the afterglow electrons Delayed External Shock scenario X-ray flares  synchrotron GeV flares  self-IC emission of flare photons scattered by afterglow electrons A. Galli-ASDC, 3 July 2007

  13. AGILE LAT sensitivity vs. AGILE and EGRET LAT: Fth~ 5·10-7 t-1 erg cm-2 s-1 t < tc, tc~22ksec Fth~3·10-9 t-1/2ergcm-2 s-1 t >tc Sensitivity @ 400 MeV z=0.1 z=1 AGILE: Fth~6·10-6 t-1 erg cm-2 s-1 t < tc , tc~3000 sec Fth~6 ·10-7 t-1/2ergcm-2 s-1 t >tc A. Galli-ASDC, 3 July 2007

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