1. Stochastic wake field particle acceleration in Gamma-Ray Bursts Barbiellini G., Longo F. (1), Omodei N. (2), Giulietti D., Tommassini P. (3), Celotti A. (4), Tavani M. (5) Gamma-Ray Burst (GRB) are major explosive phenomena of our Universe in need of an explanation. The typical light curves are characterized by short pulses, which can last from few milliseconds up to hundred of seconds. We investigate the possibility that, for specific conditions, the prompt emission from GRB can be so powerful and short-pulsed to strongly influence the surrounding plasma. Recent laboratory experiments clearly indicate that powerful laser beam pulses of tens of femtosecond duration hitting on target plasmas cause efficient particle acceleration and betatron radiation up to tens of MeV. We discuss the possibility that a very intense initial burst of radiation produced by GRBs satisfies the intensity and temporal conditions to cause stochastic wake-field particle acceleration in a surrounding plasma of moderate density. We consider a simple but realistic GRB model for which particle wake-field acceleration can first be excited by a very strong low-energy precursor, and then be effective in producing the observed prompt X- ray and gamma-ray GRB emission. We also briefly discuss some of the consequences of this novel GRB emission mechanism. (1) University & INFN – Trieste (2) INFN Pisa (3) University of Pisa (4) SISSA Trieste (5) IASF/INAF Rome – University of RomeII GRB AFTERGLOW EMISSION THE FIREBALL MODEL THE COMPTON TAIL PHENOMENUM IMPLICATIONS PLASMA WAKEFIELD ANALOGY CONCLUSIONS GRB PROMPT EMISSION - Brief intense episode of gamma-ray emission in the 10 keV – 10 MeV energy range with 10 -6 erg cm -2 fluence - Isotropic direction in the sky - Non thermal spectrum APPLICATION TO GRB Jetted structure of GRB Presence of Material around GRB Compton tail measurement relevant for GRB source mechanism Plasma acceleration mechanism Plasma Physics and Astrophysics GRB PROGENITOR COMPTON TAIL INTERPRETATION Temporal behaviour Spectral shape Spatial distribution Costa et al. (1997) Kippen et al. (1998) Djorgoski et al. (2000) - Emission in the X-ray to Radio band lasting for longer periods (hrs to months) - Confirmation of Cosmological distance - Jetted nature of emission Relativistic motion of the emitting region Shock mechanism converts the kinetic energy of the shells into radiation. Internal Shocks  Source activity  Synchrotron Emission  Rapid time Variability  Low conversion efficiency External Shock  Synchrotron & SSC  High conversion efficiency  Not easy to justify the rapid variability Image credits to CXO/NASA - Long Burst progenitor in Massive rotating stars - Evidence from GRB localized in Star Forming regions - Evidence from SN explosion Q = cts/peak cts  BRIGHT GRB  DIM GRB  Search for Post Burst emission in prompt GRB energy band  Looking for high energy afterglow (overlapping with prompt emission) for constraining Internal/External Shock Model  Sum of Background Subtracted Burst Light Curves  Tails out to hundreds of seconds decaying as temporal power law  = 0.6  0.1  Common feature for long GRB  Not related to presence of low energy afterglow  3 equally populated classes  Bright bursts  Peak counts >1.5 cm -2 s -1  Mean Fluence 1.5  10 -5 erg cm -2  Dim bursts  peak counts < 0.75 cm -2 s -1  Mean fluence 1.3  10 -6 erg cm -2 Barbiellini et al. (2004) MNRAS 350, L5  “Prompt” luminosity  Compton “Reprocessed” luminosity  “Q” ratio  Connaughton (2002), ApJ 567, 1028  Bright bursts (tail at 800 s)  Peak counts >1.5 cm -2 s -1  Mean Fluence 1.5  10 -5 erg cm -2  Q = 4.0  0.8 10 -4 (5  ) fit over PL   = 1.3  Dim bursts (tail at 300s)  peak counts < 0.75 cm -2 s -1  Mean fluence 1.3  10 -6 erg cm -2  Q = 5.6  1.4 10 -3 (4  ) fit over PL   =2.8 R = 10 15 cm n ~10 8 -10 9 cm -3  R ~ R  ~ 0.1 - Presence of dense material in front of GRB - Which is the effect for GRB emission? (Ta Phuoc et al. 2005) Laser Pulse t laser = 3 10 -14 s Laser Energy = 1 Joule Gas Surface = 0.01 mm 2 Gas Volume Density = 10 19 cm 3 Power Surface Density  W = 3 10 18 W cm -2 Stochastic Factor Scaling Relations Power Density 1 2 3