isapp (paris – 2012)
DESCRIPTION
ISAPP (Paris – 2012). Background. Using gamma-flares for cosmic neutrino analysis in ANTARES. Agustín Sánchez-Losa IFIC (CSIC- Universitat de València ) e-mail: [email protected]. Credit: Damien Dornic (CPPM-France). Sample for source 3C454.3. - PowerPoint PPT PresentationTRANSCRIPT
ISAPP (PARIS – 2012)
Agustín Sánchez-LosaIFIC (CSIC-Universitat de València)e-mail: [email protected]
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.
[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.
Neutrinos & Gamma-Rays ANTARES
Flare Analysis in ANTARES
BackgroundDetection Principle
• 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
nm
γcθc = 42º
L12
L10
L8
L6
L11
L4
L7
L9 L5
L1L3
L2
source name
ANTARESvisibility
time PDF(MJD+54000)
Live time (days) N(5σ) Nobs
Fluence U. L.GeV/cm2
(**)
0208-512 1.0 712-5, 722-4, 745-7, 750-2,753-7, 764-74, 820-2 8.8 4.5 0 2.8
0235+164 0.41 710-33, 738-43, 746-64, 766-74, 785-7, 805-8, 810-2 24.5 4.3 0 18.7
1510-089 0.55 716-9, 720-5, 726-35, 788-90, 801-3 4.9 3.8 0 2.8
3C273 0.49 714-6, 716-8, 742-5 2.4 2.5 0 1.1
3C279 0.53 749-51, 787-809, 812-5, 817-21, 824-6 13.8 5.0 1 8.2
3C454.3 0.41 713-51, 761-5, 767-9, 784-801 30.8 4.4 0 23.5
OJ287 0.39 733-5, 752-4, 760-2, 768-70,774-6, 800-2, 814-6 4.3 3.9 0 3.4
0454-234 0.63 743-5, 792-6, 811-3 6.0 3.3 0 2.9
WComae 0.33 726-9, 771-3, 790-2, 795-7, 815-7 3.9 3.8 0 3.6
2155-304 0.68 753-5, 766-8, 799-801, 828-30 3.1 3.7 0 1.6
Results for 2008 data (*)(*) 61 days(**) Neyman
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.
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.
Using gamma-flares for cosmic neutrino analysis in ANTARES
Credit: Damien Dornic (CPPM-France)
Sample forsource
3C454.3
Background image: photo by Agustín Sánchez-Losaof a calm Mediterranean Sea at the ANTARES site
during the sea operation of the 19th June, 2012.
All reconstructed events
Selected events
Sep-Dec 2008~61 days
Credit: Damien Dornic (CPPM-France)
Credit: ANTARES Collaboration
νγ
AGN
FERMI/LAT
ANTARES
HADRONIC SCENARIO
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.
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.
AGN’s flare typical range
δ = -40°
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
Credit: Damien Dornic (CPPM-France)
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.
Results forsource 3C279
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.
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.
Credit: Damien Dornic (CPPM-France)
Stud
ied
per
iod
1000 days of 3C454.3
denoised light curve
Preliminary
Credit: ANTARES Collaboration
ANTARES events since 2008