the effect of neutrinos on the initial fireballs in grb ’ s talk based on astro-ph/0505533 (hk and...

The effect of neutrinos on the initial fireballs in GRB’s

Talk based on astro-ph/0505533 (HK and Ralph Wijers)

Hylke KoersNIKHEF & University of Amsterdam

Amsterdam, The Netherlands

What’s a gamma-ray burst?What’s a gamma-ray burst?

Hylke Koers, NIKHEF, AmsterdamHylke Koers, NIKHEF, Amsterdam

catastrophic event

fireball (Cavallo and Rees 1978) shocks: particle acceleration

electrons: 1 MeV photons

protons: 1014 eV neutrinos(Waxman & Bahcall 1997)

Key featuresTotal energy ~ 1052 ergRapid variability: compact sourceBeamingLorentz factors ~ 300

Overview of generic model

106.5 cm 1012 -1014 cm

MotivationMotivation


Assumptions for fireballSpherical symmetryThermal 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 fireballThe fireball


fire· ball [‘fIr-”bol]: A tightly coupled plasma of photons, electron-positron pairs (and neutrinos)

Ballpark numbersEnergy ~ 1052 ergRadius ~ 106.5 cmTemperature ~ 2· 1011 K (20 MeV)

e

np

~ 1035 cm-3

(thermodynamics)

~ 1032 cm-3 (baryon loading: 1 TeV / baryon)

Dynamics: E R = const (Shemi & Piran 1990)

The fireball: electrons and positronsThe fireball: electrons and positrons


Net and total number density

ne := ne- - ne+ ne := ne- + ne+

Charge neutrality

Low baryon density small chemical potential

ne = np = Ye nB

ne « ne e « kBT

Environment:High temperatureLow nucleon densityVery small electron chemical potential

Neutrino physics: processesNeutrino physics: processes


Leptonic processesPhotoneutrino: e + e + + Plasma process: + Pair annihilation: e+ + e- +

Scattering: e + e +

Nucleonic processesElectron capture p + e- n + e

Positron capture n + e+ p + e

Together: non-degenerate URCA

Inverse: absorptionScattering: N + N +

Neutrino physics: emissivityNeutrino physics: emissivity


Neutrino physics: mfpNeutrino physics: mfp


The neutrino physics is dominated by leptonic processes

Neutrino physics: parametersNeutrino physics: parameters


Electron-positron pair annihilation (e+e- )All flavours, though mostly electron-typeAs much neutrinos as antineutrinosEmissivity scales as T9 (Dicus 1972)

Q = 3.6· 1033 erg s-1 cm-3 T

1011 K

9

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 stronglyNeutrinos and antineutrinos same mfpMean free path scales as T-5 (Tubbs and Schramm 1975)

= 107 cm -5T

1011 K

Optical depth

= R /

E5/4 R-11/4

Neutrino physics: phase diagramNeutrino physics: phase diagram


, neutrinos: 14/43 ~ 33%

e neutrinos: 7/29 ~ 24%

E R = const

Neutrino physics and emissionNeutrino physics and emission


Physics for ‘standard’ initial conditions:Thermodynamic equilibriumEqual amount of neutrinos and antineutrinos

Hydrodynamic expansion: thermal energy kinetic energyContinous cooling not important

e: 24%

,: 33%

Neutrino emission:Two decoupling bursts, effectively one IsotropicTotal energy:

Thermal spectrum: Tobs ~ T0 (blueshift: Goodman 1986)

E = 3· 1051 erg

11/16E0

1052 ergR0

106.5 cm

< E > = 56 MeV -3/41/4E0

1052 ergR0

106.5 cm

Neutrino emission: detectabilityNeutrino emission: detectability


Can we detect a neutrino source withTotal energy 1051 - 1053 ergMean energy 50 - 100 MeVIsotropic

Detection feasible up to 4 Mpc (rough S/N estimate)

Investigated by Halzen et al. for Amanda/IceCUBEDetection channel: p + e n + e+ Positron emits Cerenkov lightDetection by PMT’s (very large attenuation length in ice)


The effect of neutrinos on the fireballFireball starts neutrino-opaqueThermal equilibrium is established rapidlyNeutrinos follow the standard hydrodynamical evolutionCooling is never fast enough to prevent an explosion

Neutrino emissionTwo decoupling bursts, effectively oneContinuous cooling not importantRoughly 30% of the initial energy carried awayIsotropicNeutrinos and antineutrinos of all flavoursMean energy roughly 60 MeVDetection feasible up to 4 Mpc (Halzen & Jaczko 1996)

ConclusionConclusion

Conversion back to heatShocks accelerate particles,emit radiation

Fireball expansionKinetic energy of baryons

Energy flowEnergy flow


Transfer to fireballThermalPoynting flux

Black hole-accretion disk

Energy reservoirBH spin energyAccretion disk binding energy

the effect of neutrinos on the initial fireballs in grb ’ s talk based on astro-ph/0505533 (hk and...

Documents

e e scattering

e e plasma process

processeshylke koers

emissivityhylke koers

detectabilityhylke koers

mfphylke koers

fireballhylke koers

positronshylke koers