# Presentation: 154992

## The effect of neutrinos on the 

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

- Talk based on astro-ph/0505533 (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: 1014 eV neutrinos
- (Waxman & Bahcall 1997)

**Key features******Total energy ~ 1052 erg****Rapid variability: compact source****Beaming****Lorentz factors  ~ 300

*Overview of generic model*

-  106.5 cm

-  1012 -1014 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 	~ 1052 erg
****Radius 	~ 106.5 cm
****Temperature	~ 2· 1011 K (20 MeV)

## The fireball: electrons and positrons

- Hylke Koers, NIKHEF, Amsterdam

**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 capture	p + e-		n + e
****Positron capture	n + e+		p + e
****Together: non-degenerate URCA
****Inverse: absorption
****Scattering:		N + 		N + 

- vs

## 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 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
****Neutrinos and antineutrinos same mfp
****Mean free path scales as T-5 (Tubbs and Schramm 1975)

**Optical depth ******
**** = R / 
-    E5/4 R-11/4

## Neutrino physics: phase diagram

- Hylke Koers, NIKHEF, Amsterdam

## 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

## Neutrino emission: detectability

- Hylke Koers, NIKHEF, Amsterdam

**Can we detect a neutrino source with******Total energy 1051 - 1053 erg****Mean energy 50 - 100 MeV****Isotropic

*?*

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

## Conclusion

- 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)

## Energy flow

**Conversion back to heat**
- Shocks accelerate particles,emit radiation

**Fireball expansion**
- Kinetic energy of baryons

- Hylke Koers, NIKHEF, Amsterdam

**Transfer to fireball**
- ThermalPoynting flux

*Black hole-accretion disk*

**Energy reservoir**
- BH spin energy
- Accretion disk binding energy