GRB fireballs:
neutron loaded explosions

Elena ROSSI

MPA--->JILA

collaborators:

Andrei M. Beloborodov & Martin J. Rees

Outline

Brief introduction on GRB

Nuclear composition of engine+jet: n/p>1

Theory of GRB outflows with neutrons

conclusions

The internal-external shock scenario

Inner engine releases unsteady flow of ~1052 erg

Shells with different Gcatch up at R ~ R0 G2 ~ 1013 cm

Shock waves (internal) accelerate electrons and generate magnetic fields: synchrotron emission

At R ~ 1016 cm an (external) shock is driven in the interstellar medium

Synchrotron emission but at lower n and decreasing – frequencies

GRB outflows have neutrons

Current engine models naturally predict

n/p>1 (Ye<0.5)

(Derishev et al 99, Beloborodov 03, Pruet at al 03)

GRB jets are powered by a high rate accretio

disk of ~ Msun per sec around a solar mass BH

(Woosley 93, Eichler et al. 89, Janka et al. 99&01,

Vietri&Stella 98, Zhang&Fryer 01 , Fryer et al. 99)

Jets are born in neutron rich sites
the accretion disk at r<30Rs has:
r ~1011 g/cm3 and T~ few 1010 K

Beloborodov 03

Pruet, Woosley & Hoffman 03

nuclei

n/p<1

n/p>1

free

Baryonic composition of GRBs

Escape vs neutralisation timescale:

te+p> tesc so

n/p jet = n/p engine

Little Nucleosynthesis:

free p & n with n/p>1

(Beloborodov 03, Lemoine 02, Pruet et al 03)

From Pruet et al 03

How do neutrons affect the outflow dynamics and thermodynamics of GRB fireballs?

Standard matter dominated fireball:
protons+electrons+radiation

For most of the time is a COLD

COASTING outflow

R0=107 cm

L=1052 erg/s

h=200

p

e

r

Rossi, Beloborodov, Rees 05

h=E/Mbc2

Rees&Meszaros ...

Fireball theory with neutrons

Outflow with p+e+r+n

r⇔e by Compton Scattering

e⇔p by Coulomb Collision

p⇔n by strong collision

p⇔pn (n⇒pn+e+ne)by plasma instability

tb=900 s ---> Rb= c tbGn

n

brel=tnp/td

n

Gp

Gn

b decay

p

n

Solving for dynamics and thermodynamics

8 unknown : Gn Gp Tn Tp Te Tr np nn

8 coupled equations :

1) energy conservation (T mn,n=0)

2) mass conservation (F n,n =0)

3) Mp=f(Mn) , decay changes n/p

4) Gn=f( Gp) accelerating force of p on n

5-6-7-8) dEi=dQi-Pi dV , i=r,e,p,n

Rossi, Beloborodov & Rees 05

p

e

r

n

p

h=300

n/p=10

L=1052 erg/s

R0=107 cm

p

e

r

n

p

h=300

n/p=10

L=1052 erg/s

R0=107 cm

Rsep≥2G2nDR~2 1016 cm

p

e

r

n

p

h=300

n/p=10

L=1052 erg/s

R0=107 cm

p Grel n

p

e

r

n

p

h=300

n/p=10

L=1052 erg/s

R0=107 cm

r

p

e

r

n

p

h=300

n/p=10

L=1052 erg/s

R0=107 cm

p

e

r

n

p

h=300

n/p=10

L=1052 erg/s

R0=107 cm

p Grel p

n

b

e-

n∝e-R/Rb

Increasing h = decreasing Mb

h=300

h=3000

increasing n/p

black=10

red=4

blue=1

Collimated outflows

h=300

107

109

108

L=1052erg

Long vs short GRBs

Rsep≈2 G2n c Dt ;

Rb= c Gn tb = 8 1015 cm

Rd= 1.3 1017 E1/353 G2(- 2/3) n0(- 1/3) cm

Long : Rb<Rsep<Rd

Short : Rsep < Rb<Rd --> refresh shocks and no b heating

Conclusions

Fireballs are likely neutron loaded

This influences dynamics and thermodynamics of the proton component

The heating and deceleration depends on h and especially on n/p: link with the accretion disk

Nucleosynthesis
(Beloborodov 03, Lemoine 02, Pruet et al 03)

Photon-to-baryon ratio:

Exp. Timescale at NSy:

n/p ratio prior to NSy:

Big Bang GRB

~3 109 ~8 104

~100 s ~10-3s

n/p=1/7 n/p>1

GRB has marginally successful nucleosynthesis

a/(p+n)~0.01-0.1 ---> jet with free p & n with n/p>1

2004-12-09T16:16:48