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ISAPP (Paris – 2012). Background. Using gamma-flares for cosmic neutrino analysis in ANTARES. Agustín Sánchez-Losa IFIC (CSIC- Universitat de València ) e-mail: Credit: Damien Dornic (CPPM-France). Sample for source 3C454.3.

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ISAPP (Paris – 2012)


Using gamma-flares for cosmic neutrino analysis in ANTARES


IFIC (CSIC-Universitat de València)


Credit: Damien Dornic (CPPM-France)

Sample for

source 3C454.3

Transient sources, like AGNs or Gamma Ray Bursters, are among the most promising candidates for neutrino telescopes. One of the advantages for detecting a signal from them is that the neutrinos would be emitted in a short time window, so the rejection of background is much more efficient. There are two sources of background: the muons and the neutrinos produced by cosmic rays in the atmosphere. Atmospheric muons can be drastically reduced by selection only upgoing events, so that the Earth filters them. Atmospheric neutrinos are an irreducible background. As mentioned above, a case particularly favorable concerning background rejection occurs for transient sources, since in addition to the fact that the signal would be concentrated around the source position, it also would be correlated in time with the flare or burst. Considering a proportional correlation in the cosmic source of neutrino and gamma rays generation, light curves from different monitored sources and gamma flares detected can improve the discovery chances in a multi-messenger analysis. First results from ANTARES flare analysis using FERMI light curves are also presented. There are also ongoing studies for the last years data, including coordination with flares observed in X-rays by SWIFT and ASM.













Neutrinos & Gamma-Rays



The ANTARES detector is a neutrino telescope placed at the bottom of the Mediterranean Sea (42°48 N, 6°10 E), at a depth of 2475 m, connected by a submarine cable of 42 km to the shore in Toulon (France). This cable connects through a junction box 12 lines which are separated by 60–70 m and vertically suspended by a buoy. Each line has 25 floors spaced by 14.5 m, except for line 12 which has only 20 floors. A floor consists of a triplet of optical modules (OMs) each one housing a photomultiplier (PMT) facing 45° downwards. The full detector is a tri-dimensional array of 885 PMTs [3] [4] which was completed in 2008 when the last line was connected.

The full detector conforms a neutrino telescope with an angular resolution of 0.3° for neutrinos at 10 TeV and a volume of 0.1 km3, making it the largest neutrino telescope in the northern hemisphere, and the largest submarine telescope in the world ever built up to now.






Neutrinos are mainly detected via the Cherenkov light induced by relativistic muons produced in the detector surroundings by CC interactions of muon neutrinos with nuclei in water. The signals from the Cherenkov photons detected by the PMTs are digitized (‘hits’) and sent to the shore station for reconstruction and physics analysis.

The main background in a neutrino telescope comes from the flux of surviving down-going muons produced by the CR interactions in the atmosphere, and can be significantly reduced by only selecting the up-going tracks. On the other side, the atmospheric neutrino background is irreducible, and only clusters of events can reveal the existence of cosmic neutrino sources.

Neutrino production on astrophysical sources is linked to CRs by means of the so called hadronic models [1]. In these models, accelerated CRs, mainly protons, interact in the surroundings with the environmental photons predominantly via the ∆ resonance producing neutrinos and photons. So CRs, GRs and neutrinos are correlated and can be used together in a multi-messenger approach, allowing flux limits predictions between them and confirming or excluding theoretical models for the production mechanisms.

Neutrino telescopes, like ANTARES, can use the data provided by the gamma telescopes, like FERMI/LAT [2], performing a multi-messenger analysis of the astrophysical sources, like AGNs, by combining the light curves emission fluxes with the detected neutrinos information.

Detection Principle


θc = 42º

Flare Analysis in ANTARES


  • In order to decrease the background contamination in the reconstructed events in ANTARES, some quality cuts in the parameters can be applied for the optimization of an analysis:
  • Only up-going events (θ > 90°)
  • A reconstructed track’s error lower than 1° (β < 1°)
  • High track’s fit quality parameter (Λ > -5.4)
  • A flare analysis was performed for the reconstructed events in Sep-Dec 2008, with an unbinned method based on a likelihood ratio maximization, where the data is parameterized as a two components mixture of signal and background.


  • Credit: ANTARES Collaboration
  • Credit: Damien Dornic (CPPM-France)
  • A neutrino interacts in the surroundings of the detector producing a muon
  • The Cherenkov radiation induced by the muon is detected by the PMTs of the neutrino telescope

All reconstructed events

Sep-Dec 2008

~61 days

Selected events

In the likelihood evaluation, the time info is included to estimate the probability of an event to be background or come from an astrophysical source. That time info is given by the light curves of the selected 10 AGNs, provided by FERMI/LAT. Over those light curves a flaring period is characterized and used for that purpose.

ANTARES events since 2008


Results for 2008 data (*)

(*) 61 days

(**) Neyman

  • The use of the time info in the likelihood decreases the signal required for a 5σ discovery as a function of the flare duration, giving an improvement of a factor 2-3 with respect to a time integrated analysis.
  • Despite the absence of a discovery in the flare analysis of 2008 the prospects are very positive:
  • More than 3000 neutrino candidates have been detected by ANTARES since 2008.
  • Very important flares have been detected by Fermi in the last 2 years.
  • New, improved analaysis with a denoising of the light curve are ongoing.

Credit: Damien Dornic (CPPM-France)

Credit: Damien Dornic (CPPM-France)

δ = -40°

Results for

source 3C279

  • Credit: ANTARES Collaboration

Studied period

AGN’s flare typical range

In the ANTARES flare analysis for 2008 data (61 days) only one neutrino event was found during a flaring period being compatible with the source position. This is the most significant observation found, with a p-value of about 10% after trials, still compatible with a background fluctuation. Limits on the neutrino fluence have been obtained for the sources.

  • 1000 days of 3C454.3
  • denoised light curve

Averaged number of events required for a 5σ discovery (50% prob) produced in one source as a function of the width of one flare period

[1] T.K. Gaisser, F. Halzen, T. Stanev, Phys. Rep. 258 (1995) 173; J.G. Learned, K. Mannheim, Ann. Rev. Nucl. Part. Sci. 50 (2000) 679; F. Halzen, D. Hooper, Rep. Prog. Phys. 65 (2002) 1025.

[2] A.A. Abdo et al., Astrophys. J. 722 (2010) 520.

[3] J.A. Aguilar et al., ANTARES Collaboration, Nucl. Instrum. Meth. A 570 (2007) 107.

[4] J.A. Aguilar et al., ANTARES Collaboration, Astropart. Phys. 34 (2011) 539.

Background image: photo by AgustínSánchez-Losa

of a calm Mediterranean Sea at the ANTARES site

during the sea operation of the 19th June, 2012.