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

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

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

Thompson & Madau (2000), Beloborodov (2002)

Beloborodov (2002)

Beloborodov (2005)

GRB blast wave at the deceleration stage

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

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)

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)

GRB 941017 Gonzalez et al. 2003

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