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Individual GRB sensitivity of the cubic-kilometre deep-sea neutrino telescope KM3NeT

Individual GRB sensitivity of the cubic-kilometre deep-sea neutrino telescope KM3NeT. Damien Dornic (CPPM/Marseille). VLVNT08 - 23/04/2008. Gamma ray bursts.

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Individual GRB sensitivity of the cubic-kilometre deep-sea neutrino telescope KM3NeT

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  1. Individual GRB sensitivity of the cubic-kilometre deep-sea neutrino telescope KM3NeT Damien Dornic (CPPM/Marseille) VLVNT08 - 23/04/2008

  2. 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 …)

  3. Time constrain + Positionning ~ Background free Neutrinos detection from GRBs • Neutrino telescopes are well adapted to study prompt emission mechanisms: • Continuous data taking • Special trigger based on GCN alert with a low threshold…

  4. a = -0.6 b = -3.1 Ep = 720 keV Prompt emission spectra All GRB photon-spectra described using a broken power-law • 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 • [D.Band et al, Astrophys. J. 413, 281 (1993)] • [D.Guetta et al, Astropart. Phys. 20, 429 (2004)]

  5. “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

  6. Neutrino production • 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 • 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)

  7. : Photon fluence (erg.cm-2) : Proton efficiency : Neutrino break energy : Burst duration : Pion synchrotron break energy Muon neutrino spectrum To determine the neutrino flux, the redshift is needed

  8. Application to SWIFT data 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

  9. Maximum spectrum Minimum spectrum Gamma ray spectrum 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 GRB071227 → z = 0.383 → Fγ = 2.2 10-7 erg.cm-2 → T90 = 1.8s

  10. 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

  11. Event rate for a km3 detector 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°

  12. Event rate for a km3-scale detector For the 58 GRBs with a redshift and visible as up-going in the ANTARES site Signal Noise For individual burst : Event : ~ 5.10-3 Background: ~ 3 10-6 With an error bar of ~ ±1 order of magnitude Rate: ~3 GRBs/day → 0.5 GRB/ (Gpc3.yr)

  13. Minimal fluence to detect a single GRB → Criteria to detect an individual burst 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

  14. Minimal fluence to detect a single GRB → Criteria to detect an individual burst For a standard GRB (Lγ ~ 1051 erg/s) → « Horizon of detection » ~ 150 Mpc SWIFT BATSE Some GRBs passed the minimal fluence criteria: BATSE ~ 6 / 2704 SWIFT ~ 1 / 297 (GRB080319B)

  15. Summary • All this work is consistent with previous study based on BATSE • 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)

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