Transcript Transparencies

Blast waves from GRBs
Andrei M. Beloborodov
Columbia University
1. Blast wave
2. GeV – TeV flashes
Meszaros, Rees (1993)
Sari, Piran (1999)
Self-similar adiabatic
blast wave:
m G 2 = const
(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
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Rb ~ tb Gn c ~ 10
(G n /300) cm
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.
(Akerlof et al. 1999)
 Compton cooling of the flash
electrons by GRB photons and
 Production of GeV-TeV flash much
stronger than its optical counterpart.
Expected GeV-TeV flashes
1. 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 ( E1/2 ).
2. The flash is a few times longer than the prompt GRB.
3. The flash has a smooth light curve.
(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
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(R ~ 10
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-- blast wave is loaded with e+/- pairs (R ~ 10
cm)
cm)
-- survived neutrons leak out of the decelerated ejecta
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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.