Neutrinos as probes of gamma-ray bursts

Hylke Koers, Service de Physique Théorique, UL Brussels

Neutrinos as probes ofgamma-ray bursts

Hylke Koers

Based on work in collaboration with:Ralph Wijers (API Amsterdam)Asaf Pe’er (Giacconi fellow, Hubble Space Telescope Science Institute)Dimitrios Giannios (Max-Planck-Institute for Astrophysics Garching)

Service de physique théorique, UL Brussels


Outline

Fireball neutrino cooling

Neutrino production in np collisions

Neutrino emission from choked GRBs

A gamma-ray burst primer


Motivation

Interesting for modelling: unresolved observations and extreme properties

Candidate sources of cosmic rays

Candidate sources of neutrinos

Probes of the universe up to z ~ 5, constraining DM and DE

Speculative ideas: constraining Lorentz invariance through arrival times, ... (?)


A GRB primer: observational landmarks

Some observational landmarks:

’60s: Discovery of very energetic flashes of gamma rays. (military VELA satellites) – distance scale?

>1991: Isotropic distribution found (BATSE all-sky monitor from CGRO)

1997: Afterglow observations establish cosmological scales (BeppoSAX satellite)

1998: First identification of a contemporaneous SN – GRB (BeppoSAX / BATSE)

2004: SWIFT satellite observes shallow decay phase, late

energetic flares, and other unexpected phenomena


A GRB primer: prompt emission

Key features of the prompt emission

Irregular lightcurves:“if you’ve seen one GRB...”

Rapid varibility, up to 10-3 sec.

Duration from 10-2 s – 103 s, subdivided intolong GRBs (~20 sec) and short GRBs (~0.2 sec)

Non-thermal spectrum (broken power-law),peaking around ~250 keV; occasionally extending to very high energies (> GeV... TeV?)


A GRB primer: afterglow

Key features of the afterglow

Broad-band spectrum over many decades inenergy (radio, optical/IR, X-ray)

Characteristic break energies compatible with synchrotron emission

Slowly declining (typically power-law) lightcurve(sometimes detectable up to years


A GRB primer: the fireball model

Acceleratingphase(108 cm)

Fireball accelerates to relativistic velocities ~ 300by radiation pressure; stops due to energy constraints(baryonic load)

Initial phase(106.5 cm)

Catastrophic event: core-collapse of a massive star (long GRB): Formation of black hole + accretion disk system which launches a fireball

Interaction with external environment: afterglowAfterglowphase (1016 cm)

Coastingphase (1012 cm)

Energy dissipation (shock acceleration):gamma-ray burst

[Cavallo & Rees 1978; Paczynski 1986; Mészáros & Rees 1992, 1993]

Key featuresTotal energy ~ 1052 erg

Lorentz factors ~ 300Collimation

Small baryonic load


A GRB primer: open questions

Neutrinos are expected to be very useful probes to gain insight in these issues!


Hylke Koers, Service de Physique Theorique, UL Brussels

Important (partly) unsolved questions:

How are the jets formed?

What is the nature of the outflow?Dominated by thermal energy (=fireball?)or by electromagnetic energy?

How is shock-acceleration realized?




Outline




Can neutrino cooling stop a developing GRB?[Koers & Wijers, MNRAS, 364, 934, 2005]



Fireball cooling: the fireball

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

Environment Temperature: T ~ 1011 K (20 MeV) Electrons, positrons: ne ~ 1035 cm-3

Baryons: nB ~ 1032 cm-3

Neutrino physics dominated by leptonic processes

DynamicsThe fireball expands by radiation pressure to relativistic velocities.

e±

pn


Fireball cooling: neutrino phase diagram

[HK & Wijers 2005]

rapid cooling

The fireball is transparant in regions of fast neutrino creation. Here neutrinos just follow the usual hydrodynamic evolution.

Roughly 30% of the initial energy is released as a burst of ~60 MeV neutrinos


Outline

Can we use neutrinos (or gamma rays) from nucleonic collisions to discriminate between models?[Koers & Giannios, A&A, 471, 395, 2007]






NP decoupling: characteristic radii

Accelerating phase Coasting phase

Fireball model:

AC (magnetic) model:


NP decoupling: neutrinos and gamma rays

fluence fromburst at z=0.1

peak energy

AC modelFireball (FB) model

Both fluence and energy are below IceCube sensitivity!

prompt GRB(internal shocks)

np gamma rays(fireball only!)

~100 keV ~10 GeV


Outline

Can neutrino emission indicate the existenceof choked GRBs?[Koers & Wijers, arXiv: 0711.4791]






Choked GRBs: model

Motivation:Observed SN – GRB connection

Missing ingredient in SN modelling Ubiquity of astrophysical jets

Hypothesis: suppose that a (large) fraction of supernovae is accompanied by GRB-like outflows that stops below the surface [Mészáros & Waxman 2002]

No gamma-ray emission Potential source of neutrinos

(largely unconstrained)


Choked GRBs: protons

Proton energy losses

Synchrotron radiation Photopion ...

Proton shock acceleration

[Razzaque, Mészáros & Waxman 2003, 2004, 2005; Ando & Beacom 2005]

Scheme: accelerate protons, create mesons,decay to neutrinos


Choked GRBs: protons

Maximum energy (in jet frame)


Choked GRB: mesons

Cooling break


Choked GRB: mesons

Cooling break

Maximum energy(in jet frame)


Choked GRBs: neutrino spectrum

Neutrino spectrum from meson (and muon) decay:

cooling break maximum energy

(at Earth)

Strong increase in high-energy neutrinos!


Choked GRBs: detection prospects

NB: optimistic case ofefficient meson injection


Conclusions

Neutrino emission is an interesting and promising way to probe the physics of GRBs.

However it remains a challenging task to identify concrete realizations of this potential.

Documents

Neutrinos as probes of gamma-ray bursts