The effect of neutrinos on the initial fireballs in GRB ’ s Talk based on astro-ph/ (HK and Ralph Wijers) Hylke Koers NIKHEF & University of Amsterdam Amsterdam, The Netherlands

What ’ s a gamma-ray burst? Hylke Koers, NIKHEF, Amsterdam catastrophic event fireball (Cavallo and Rees 1978) shocks: particle acceleration electrons: 1 MeV photons protons: eV neutrinos (Waxman & Bahcall 1997) Key features  Total energy ~ erg  Rapid variability: compact source  Beaming  Lorentz factors  ~ 300 Overview of generic model cm cm

Motivation Hylke Koers, NIKHEF, Amsterdam Assumptions for fireball  Spherical symmetry  Thermal energy domination Look at ’ s to learn about the central engine What is the neutrino physics?  Can neutrino cooling prevent an explosion?  Can we detect neutrinos from the central engine?

The fireball Hylke Koers, NIKHEF, Amsterdam fire · ball [ ‘ fIr- ” bol]: A tightly coupled plasma of photons, electron-positron pairs (and neutrinos) Ballpark numbers  Energy ~ erg  Radius ~ cm  Temperature~ 2 · K (20 MeV)  ee n p ~ cm -3 (thermodynamics) ~ cm -3 (baryon loading: 1 TeV / baryon) Dynamics: E R = const (Shemi & Piran 1990)

The fireball: electrons and positrons Hylke Koers, NIKHEF, Amsterdam Net and total number density  n e := n e- - n e+ n e := n e- + n e+ Charge neutrality Low baryon density  small chemical potential  n e = n p = Y e n B  n e « n e   e « k B T Environment:  High temperature  Low nucleon density  Very small electron chemical potential

Neutrino physics: processes Hylke Koers, NIKHEF, Amsterdam Leptonic processes  Photoneutrino:e  +  e  + +  Plasma process:  +  Pair annihilation:e + + e -  +  Scattering:e  + e  + Nucleonic processes  Electron capturep + e -  n + e  Positron capturen + e +  p + e  Together: non-degenerate URCA  Inverse: absorption  Scattering:N + N +

Neutrino physics: emissivity Hylke Koers, NIKHEF, Amsterdam

Neutrino physics: mfp Hylke Koers, NIKHEF, Amsterdam The neutrino physics is dominated by leptonic processes

Neutrino physics: parameters Hylke Koers, NIKHEF, Amsterdam Electron-positron pair annihilation (e + e -  )  All flavours, though mostly electron-type  As much neutrinos as antineutrinos  Emissivity scales as T 9 (Dicus 1972) Q = 3.6 · erg s -1 cm -3 T K 9 Creation rate parameter   = t c /t e = E c s / V Q R  E -5/4 R 11/4 Scattering off electrons and positrons (e   e  )  Electron-type neutrinos are bound more strongly  Neutrinos and antineutrinos same mfp  Mean free path scales as T -5 (Tubbs and Schramm 1975) = 10 7 cm -5 T K Optical depth   = R /  E 5/4 R -11/4

Neutrino physics: phase diagram Hylke Koers, NIKHEF, Amsterdam ,  neutrinos: 14/43 ~ 33%e neutrinos: 7/29 ~ 24%E R = const

Neutrino physics and emission Hylke Koers, NIKHEF, Amsterdam Physics for ‘ standard ’ initial conditions:  Thermodynamic equilibrium  Equal amount of neutrinos and antineutrinos  Hydrodynamic expansion : thermal energy  kinetic energy  Continous cooling not important e : 24% ,  : 33% Neutrino emission:  Two decoupling bursts, effectively one  Isotropic  Total energy:  Thermal spectrum: T obs ~ T 0 (blueshift: Goodman 1986) E = 3 · erg 11/16 E0E erg R0R cm = 56 MeV -3/41/4 E0E erg R0R cm

Neutrino emission: detectability Hylke Koers, NIKHEF, Amsterdam Can we detect a neutrino source with  Total energy erg  Mean energy MeV  Isotropic Detection feasible up to 4 Mpc (rough S/N estimate) Investigated by Halzen et al. for Amanda/IceCUBE  Detection channel: p + e  n + e +  Positron emits Cerenkov light  Detection by PMT ’ s (very large attenuation length in ice)

Hylke Koers, NIKHEF, Amsterdam 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 1996) Conclusion

Conversion back to heat Shocks accelerate particles, emit radiation Fireball expansion Kinetic energy of baryons Energy flow Hylke Koers, NIKHEF, Amsterdam Transfer to fireball Thermal Poynting flux Black hole-accretion disk Energy reservoir BH spin energy Accretion disk binding energy