1. Blast waves from GRBs Andrei M. Beloborodov Columbia University • Blast wave • 2. GeV – TeV flashes

2. Meszaros, Rees (1993) Sari, Piran (1999)

4. Self-similar adiabatic blast wave: m = const 2 G (Blandford, McKee 1976)

5. Thompson & Madau (2000), Beloborodov (2002)

7. Beloborodov(2002)

11. Beloborodov (2005)

12. GRB blast wave at the deceleration stage

13. GRB blast wave at the deceleration stage 16 R ~ c ~ 10 ( /300) cm t G G n b b n

14. Optical flash in GRB 990123 • The optical synchrotron flash is emitted by relativistic electrons (Lorentz factor ~ 100 in the fluid frame). • The electrons are also exposed to the GRB photons which have ~ keV energy in the fluid frame. • Compton cooling of the flash electrons by GRB photons and • Production of GeV-TeV flash much stronger than its optical counterpart. (Akerlof et al. 1999)

15. Expected GeV-TeV flashes • Flash spectrum below GeV has the same slope as the low-energy part (0.1 MeV) of the main GRB. At higher energies –- fast-cooling spectrum ( E ). • The flash is a few times longer than the prompt GRB. • The flash has a smooth light curve. 1/2 (Beloborodov 2005)

16. GRB 941017 Gonzalez et al. 2003

17. Summary • The huge G makes the explosion qualitatively different from other known explosions: -- MeV radiation front opens the gap (R ~ 10 cm) -- blast wave is loaded with e+/- pairs (R ~ 10 cm) -- survived neutrons leak out of the decelerated ejecta and change the shock mechanism (R ~ 10 --10 cm) • Swift will observe the early stage of the explosion. A flat optical spectrum is expected from e+/- loaded blast wave. • GeV-TeV flashes must be produced by GRBs, which can be easily observed by GLAST. 15 16 16 17