Ge V emission from GammaRay Bursts Alessandra Galli

Ge. V 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 At high energies additional emission process is required, such as Inverse Compton A. Galli-ASDC, 3 July 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 Galli & Piro 2007 εB=8· 10 -2 (E 53 n)-1/4 [1+(εe/εB)1/2]1/2 · ·(ε /ε ) -1/2 T 1/4 (1+z)-1/4 e B d Relative importance of IC and synchrotron emission greater in fast cooling than in slow cooling The importance of IC increases with E 53 and n A. Galli-ASDC, 3 July 2007

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

IC Spectra 50 ksec 10 ksec 500 sec Γ 0=120, E 53 = 1. 0, n = 5, εe = 0. 2, p=2. 5, and z=1.

IC emission from afterglow: application to GRB 940217 High energy emission, 30 Me. V-30 Ge. V, 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 E 53 = 5. 0, n = 3. 0, εe =0. 07, εB = 0. 001, p = 2. 5, z =1 500 sec 5000 sec F ~t 1/3 v < νc, IC F ~t 1/8 νc, IC < v < νi, IC F~t-(10 -9 p)/8 νi, IC < ν νc, IC < νi, IC < νobs p=2. 5 γ=2. 25 A. Galli-ASDC, 3 July 2007 γ=(p+2)/2

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

Ge. V flares in association with X-ray flares -Internal Shock: Low Lorentz factor, low Thompson cross section no bright Ge. V 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 + 2 nd order IC Internal Shock 1: Synchr + self IC A. Galli-ASDC, 3 July 2007

IC emission from a thick shell fireball ISM-Fast Cooling 100 Ge. V 100 Ge. V X-ray Galli & Piro, 2007 ni. IC E 53=5, =300, n=1, e=0. 1, B=10 -4, p=2. 5, z=1, t =500 s 0 A. Galli-ASDC, 3 July 2007 ni. IC

Conclusion ü GLAST LAT – and for nearest bursts also AGILE, will be able to detect IC emission from the afterglow of Gamma. Ray Bursts; ü 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; ü X-ray flares can be attended by Ge. V flares produced by IC, that could be detected by GLAST; ü IC emission from afterglow can explain also the delayed high energy emission detected by EGRET in GRB 940217; ü We expect similar temporal profiles for X-ray and high energy flares in the context of External Shock.

Bonus Slide

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

LAT sensitivity vs. AGILE and EGRET LAT: Sensitivity @ 400 Me. V Fth~ 5· 10 -7 t-1 erg cm-2 s-1 z=0. 1 t < tc, tc ~22 ksec AGILE Fth~ 3· 10 -9 t-1/2 erg cm-2 s-1 z=1 t >tc AGILE: Fth~6· 10 -6 t-1 erg cm-2 s-1 t < tc , tc ~3000 sec Fth~ 6 · 10 -7 t-1/2 erg cm-2 s-1 t >tc A. Galli-ASDC, 3 July 2007