Damien Dornic, VLVNT08
Individual GRB sensitivity of the
cubic-kilometre deep-sea neutrino
telescope KM3NeT
Damien Dornic(CPPM/Marseille)
VLVNT08 - 23/04/2008
Damien Dornic, VLVNT08
Gamma ray bursts
…Powerful (among the most luminous sources in the Universe, up to Lγ~1052 erg/s) and highly variable (between few 10 ms to few minutes) sources of gamma rays that indicate the existence of cosmic particle accelerators
Detection: - detected first by X-ray satellites - then follow with OT
- others instruments (cherenkov telescope, neutrino telescope …)
Damien Dornic, VLVNT08
• Neutrino telescopes are well adapted to study prompt emission mechanisms: – Continuous data taking
– Special trigger based on GCN alert with a low threshold…
Neutrinos detection from GRBs
Time constrain+
Positionning~ Background free
Damien Dornic, VLVNT08
Prompt emission spectra
[D.Band et al, Astrophys. J. 413, 281 (1993)][D.Guetta et al, Astropart. Phys. 20, 429 (2004)]
Ep = 720 keV
= -0.6
= -3.1
Characteristic parameters of γ-spectra: - photon fluence - photon break Energy Eb
- low-energy spectral coefficient α - high-energy spectral coefficient β
Band function
Large parameters variability from burst to burst
All GRB photon-spectra described using a broken power-law
Damien Dornic, VLVNT08
“Fire ball” phenomenology
Prompt gamma ray (GRB it self) is due to the synchrotron radiation of electron acceleration by DSA in the internal shocks in the jet
Then, interaction with ISM → afterglow
Damien Dornic, VLVNT08
• Hadronic models suppose that protons are accelerated along with electrons ( mainly by Fermi acceleration)
→ With a power law spectrum with an index equal to -2
• We suppose also an equipartition of the energy between electrons (or photons) and protons
Neutrino production
• Shock-accelerated proton can directly interact with synchrotron gamma-ray photon (few 10 keV – MeV) in the fireball wind→ High energy neutrino (few 10 TeV – PeV)
)()( npEEif thpcm
ee
Damien Dornic, VLVNT08
Muon neutrino spectrum
90
2
10ln8 T
fF
dE
dNE
e
21
1
1
bb
b
b
EE
E
E
bEif
bb Eif
bEif
bb
: Neutrino break energy
: Pion synchrotron break energy
: Photon fluence (erg.cm-2)
: Proton efficiencyF
f: Burst duration90T
To determine the neutrino flux, the redshift is needed
Damien Dornic, VLVNT08
SWIFT data (from dec 2004 to yesterday):
297 GRBs detected by SWIFT
only 112 with a measured redshift
only 58 visible as up-going event in Antares site
Application to SWIFT data
Damien Dornic, VLVNT08
First step: determine the γ-spectrum parameters– BAT measures energy only between 15 and 150 keV
– We need to extrapolate to higher energy (→ MeV) using the knowledge of BATSE
• Used a fixed β index :
• Energy break: 100 and 800 keV
• Corrected the γ-ray fluence
– Propagate all instrumental and from the estimation errors
Gamma ray spectrum
7.03.03.2
GRB071227 → z = 0.383 → Fγ = 2.2 10-7 erg.cm-2
→ T90 = 1.8s
Maximum spectrum
Minimum spectrum
Damien Dornic, VLVNT08
Neutrino spectrum
GRB071227 → z = 0.383 → Fγ = 2.2 10-7 erg.cm-2
→ T90 = 1.8 s → Lγ = 9.83 1049 erg/s → Γ = 125 +/- 30 → fπ = 0.22
GRB080411 → z = 1.03 → Fγ = 2.63 10-5 erg.cm-2
→ T90 = 56 s → Lγ = 2.81 1051 erg/s → Γ = 228 +/- 30 → fπ = 0.34 {0.1-1}
Atmospheric neutrino: Volkova & al
Damien Dornic, VLVNT08
Event rate for a km3 detector
90
,T EE
effevent
th
dtdEtEdE
dNtEAN
Number of events per GRB →
Eth: Threshold in energy (1-10 TeV)
Neutrino effective area, Aeff →
To take into account the atmospheric neutrino background:
- Punctual source
- Angular resolution: ~0.2°
Damien Dornic, VLVNT08
Event rate for a km3-scale detector
For the 58 GRBs with a redshift and visible as up-going in the ANTARES site
For individual burst : Event : ~ 5.10-3
Background: ~ 3 10-6
Signal Noise
Rate: ~3 GRBs/day → 0.5 GRB/ (Gpc3.yr)
With an error bar of ~ ±1 order of magnitude
Damien Dornic, VLVNT08
Criteria to detect an individual burst
Minimal fluence to detect a single GRB →24 .104~ cmergF
Hypothesis: for long GRB, the luminosity is ~ 1051 erg/s
Mean redshift between 1 and 3
Use a mean for all the others parameters
→ recalculate the gamma-ray fluence
Damien Dornic, VLVNT08
Criteria to detect an individual burst
SWIFT BATSE
Some GRBs passed the minimal fluence criteria: BATSE ~ 6 / 2704 SWIFT ~ 1 / 297 (GRB080319B)
For a standard GRB (Lγ ~ 1051 erg/s) → « Horizon of detection » ~ 150 Mpc
Minimal fluence to detect a single GRB →24 .104~ cmergF
Damien Dornic, VLVNT08
Summary
• Detection of even a small number of neutrinos correlating with GRBs can prove without ambiguity presence of hadronic acceleration to UHE
• It is surely possible to detect individually some GRBs with a km3-scale detector (with almost a background free search)
• Contribution to the neutrino diffuse flux (by meaning all the neutrino spectrum for all the detected bursts and corrected to the solid angle) → the result is near the WB prediction (taking into account the UHECR flux)
•All this work is consistent with previous study based on BATSE