What

1
The effect of neutrinos on the initial fireballs
in GRBs
Hylke Koers NIKHEF University of Amsterdam
Amsterdam, The Netherlands
Talk based on astro-ph/0505533 (HK and Ralph
Wijers)
2
Whats a gamma-ray burst?
Generic model (see e.g. Piran astro-ph/9810256)
catastrophic event
fireball (Cavallo and Rees 1978)
shocks particle acceleration
protons 1014 eV neutrinos (Waxman Bahcall 1997)
electrons 1 MeV photons
106.5 cm
1012 -1014 cm
Key features?Total energy 1052 erg?Rapid
variability compact source?Beaming?Lorentz
factors ? 300
Hylke Koers, NIKHEF, Amsterdam
3
Energy flow
Energy reservoir BH spin energy Accretion disk
binding energy
Transfer to fireball ThermalPoynting flux
Fireball expansion Kinetic energy of baryons
Conversion back to heat Shocks accelerate
particles,emit radiation
Black hole-accretion disk
Hylke Koers, NIKHEF, Amsterdam
4
The fireball
fire ball fIr-bol A tightly coupled plasma
of photons, electron-positron pairs and neutrinos
Phenomenology ?Energy 1052 erg ?Radius 106.5
cm ?1 TeV / baryon
Environment ?Temperature T 2 1011 K (20
MeV) ?Electrons, positrons ne 1035
cm-3 ?Baryons nB 1032 cm-3
What is the neutrino physics in such an
environment? ?How fast is neutrino cooling? ?What
is the expected neutrino emission? ?Essential
parameters energy E and radius R
Dynamics the fireball expands by radiation
pressure and becomes ultrarelativistic.
Adiabatic scaling law (Shemi Piran 1990)
E R const
Hylke Koers, NIKHEF, Amsterdam
5
Neutrino physics
The neutrino physics is dominated by leptonic
processes
Electron-positron pair annihilation (ee- ?
??) ?All flavours, though mostly
electron-type ?Emissivity scales as T9 (Dicus
1972)

• Creation rate parameter ?
• ? tc/te E cs / V Q R
• ? E-5/4 R11/4

Scattering off electrons and positrons (e- ? ? e-
?) ?Electron-type neutrinos are bound more
strongly ?Mean free path scales as T-5 (Tubbs and
Schramm 1975)

• Optical depth ?
• ? R / ?
• ? E5/4 R-11/4

Hylke Koers, NIKHEF, Amsterdam
6
Neutrino phase diagram
Hylke Koers, NIKHEF, Amsterdam
7
Neutrinos physics and emission
Conclusion
The effect of neutrinos on the fireball ?Fireball
starts neutrino-opaque ?Thermal equilibrium is
established rapidly ?Neutrinos follow the
standard hydrodynamical evolution?Cooling is
never fast enough to prevent an explosion
Neutrino emission ?Two decoupling bursts,
effectively one ?Continuous cooling not
important ?Roughly 30 of the initial energy
carried away ?Isotropic ?Neutrinos and
antineutrinos of all flavours ?Mean energy
roughly 60 MeV ?Detection feasible up to 4 Mpc
(Halzen Jaczko Halzen Hooper)
Hylke Koers, NIKHEF, Amsterdam