Blast%20waves%20from%20GRBs

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Blast waves from GRBs

• Andrei M. Beloborodov
• Columbia University

• Blast wave
• 2. GeV TeV flashes

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Meszaros, Rees (1993) Sari, Piran (1999)
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Self-similar adiabatic blast wave m
const
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G
(Blandford, McKee 1976)
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Thompson Madau (2000), Beloborodov (2002)
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Beloborodov (2002)
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Beloborodov (2005)
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GRB blast wave at the deceleration stage
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GRB blast wave at the deceleration stage
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R c 10 ( /300) cm
t G G
n
b b
n
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Impact of neutrons on the afterglow light curve
--- Fast and strongly collimated
neutron component (Fan, Wei, Zhang 2004)
--- Slow and wide neutron component
in the MHD jet model of GRBs (Peng,
Konigl, Granot 2004)
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GRB 990123
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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)
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( Beloborodov 2005 )
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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 ( E
   ).
2. The flash is a few times longer than the prompt
   GRB.
3. The flash has a smooth light curve.

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(Beloborodov 2005)
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GRB 941017
Gonzalez et al. 2003
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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.

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Summary