1. C.Distefano Barcelona July 4 – 7, 2006 LNS Detection of point-like neutrino sources with the NEMO-km 3 telescope THE MULTI-MESSENGER APPROACH TO UNIDENTIFIED GAMMA-RAY SOURCES Barcelona July 4 – 7, 2006 Carla Distefano for the NEMO Collaboration LNS

2. C.Distefano Barcelona July 4 – 7, 2006 LNS Outline of the talk The NEMO project Simulation of the km 3 neutrino telescope performance Pointing accuracy Sensitivity to point-like neutrino sources Physics cases Microquasar LS 5039 SNR RXJ1713.7-3946 The NEMO project Simulation of the km 3 neutrino telescope performance Pointing accuracy Sensitivity to point-like neutrino sources Physics cases Microquasar LS 5039 SNR RXJ1713.7-3946

3. C.Distefano Barcelona July 4 – 7, 2006 LNS Neutrino telescope projects BAIKAL, AMANDA: taking data NESTOR, ANTARES, NEMO R&D:under construction ICECUBE: completion expected in 2010 KM3NET – Mediterranean: EU Design Study 2006-2008 AMANDA ICECUBE BAIKAL ANTARES 2400 m NESTOR 3800 m NEMO 3500 m In order to obtain the whole sky coverage 2 telescopes must be built The Galactic Centre is observable only from the Northern Hemisphere Small scale detectors and demonstrators km 3 scale telescopes

4. C.Distefano Barcelona July 4 – 7, 2006 LNS NEMO The NEMO Collaboration is dedicating a special effort in: search, characterization and monitoring of a deep sea site adequate for the installation of the Mediterranean km 3 ; development of technologies for the km 3 (technical solutions chosen by small scale demonstrators are not directly scalable to a km 3 ). test of prototypes in deep sea: NEMO Phase-1 in Catania realization of a marine infrastructure for the km 3 : NEMO Phase-2 in Capo Passero The NEMO Collaboration is dedicating a special effort in: search, characterization and monitoring of a deep sea site adequate for the installation of the Mediterranean km 3 ; development of technologies for the km 3 (technical solutions chosen by small scale demonstrators are not directly scalable to a km 3 ). test of prototypes in deep sea: NEMO Phase-1 in Catania realization of a marine infrastructure for the km 3 : NEMO Phase-2 in Capo Passero

5. C.Distefano Barcelona July 4 – 7, 2006 LNS The Capo Passero deep sea site The average depth is 3500 m, the distance from shore is 100 km. It is located in a wide abyssal plateau far from shelf breaks and geologically stable. Optical properties of deep sea water are the best measured among investigated sites (absorption length close to optically pure water astro-ph\0603701). Optical background is low (~30 kHz on 10’’ PMT at 0.5 s.p.e. threshold) and mainly due to 40 K decay since the bioluminescence activity is extremely low. Underwater currents are very low (2.5 cm/s) and stable. After eight years of activity in seeking and monitoring abyssal sites in the Mediterranean Sea the NEMO Collaboration has selected a site close to Capo Passero, Sicily (36° 16’ N, 16° 06’ E). The site has been proposed to ApPEC on January 2003 as candidate site for the installation of the km 3.

6. C.Distefano Barcelona July 4 – 7, 2006 LNS Seawater optical properties in Capo Passero Average values 2850÷3250 m Light Absorption and Attenuation lengths measured in Capo Passero don’t show seasonal dependence. Absorption lengths measured in Capo Passero are close to the optically pure sea water data.

7. C.Distefano Barcelona July 4 – 7, 2006 LNS Optical background was measured in Capo Passero @ 3000 m depth. Data are consistent with 30 kHz background on 10”PMT at 0.5 s.p.e. (mainly 40 K decay, very few bioluminescence). Optical data are consistent with biological measurements: No luminescent bacteria have been observed in Capo Passero below 2500 m Optical background in Capo Passero 40 K Baseline rate~ 30 kHz

8. C.Distefano Barcelona July 4 – 7, 2006 LNS Feasibility study for the km 3 telescope 1 main Junction Box 8  10 secondary Junction Boxes 60  80 towers 140  200 m between each tower 16  18 floors for each tower 64  72 PMT for each tower 4000  6000 PMTs Parameters to optimize: distances, number of towers, tower height, … Detector architecture issues Reduce the number of structures to reduce the number of underwater connections and allow operation with a ROV; Detector modularity.

9. C.Distefano Barcelona July 4 – 7, 2006 LNS NEMO Phase-1 300 m Mini-Tower compacted Mini-Tower unfurled 15 m Deployment of JB and mini-tower Sept. 2006 Junction Box NEMO mini-tower (4 floors, 16 OMs) TSS Frame Deployed January 2005 Realization of the key elements of the km 3 Validation of the technological solutions proposed Installation at 2000 m offshore Catania (LNS Underwater Test Site)

10. C.Distefano Barcelona July 4 – 7, 2006 LNS Simulated NEMO-km 3 detector 20 m 40 m Simulated Detector Geometry: square array of 81 NEMO towers 140 m between each tower 18 floors for each tower vertical distance 40 m storey length 20 m 4 PMTs for each storey 5832 PMTs - optical background 30 kHz - optical properties of the NEMO site of Capo Passero - ANTARES s/w tools used PMT location and orientation

11. C.Distefano Barcelona July 4 – 7, 2006 LNS Detector pointing accuracy: observation of the Moon shadow Moon rest frame Moon disk Event density (1 year of data taking) Detection of the deficit (The Moon Shadow) provides a measurement of: the detector angular resolution; the detector absolute orientation. The Moon absorbs Cosmic Rays  a lack of atmospheric muons is expected. 100 days needed to observe a 3  effect

12. C.Distefano Barcelona July 4 – 7, 2006 LNS Detector sensitivity to muon neutrino fluxes We compute the detector sensitivity to muon neutrinos from point-like sources: minimum muon neutrino flux detectable with respect to the background. 90% c.l. Calculation of the sensitivity spectrum: - we simulate the expected background b (atm. and  ) and we estimate the 90% c.l. sensitivity in counts (Feldman & Cousins); - we simulate a reference source spectrum (d  /d  ) 0 which produces n s counts; - we calculate the sensitivity spectrum as: -we apply the event selection in order to minimize the sensitivity. Feldman & Cousins define the sensitivity as the average upper limits for no true signal. It is the maximum number of events that can be excluded at a given confidence level.

13. C.Distefano Barcelona July 4 – 7, 2006 LNS Atmospheric muon and neutrino background Atmospheric neutrinos: upward tracks are good neutrino candidates; event direction and energy criteria can be used to discriminate background from astrophysical signals. Atmospheric muons: down-going muons are several orders of magnitude more than neutrino-induced muons; up-going background events are due to mis- reconstructed (fake) tracks; quality cuts applied to reject mis-reconstructed tracks. ANTARES

14. C.Distefano Barcelona July 4 – 7, 2006 LNS Event simulation  exp. events/year 17.1·10 7 1.55.7·10 4 2163.5 2.51.29 Atm. (1°) 1.06 Atm.  (1°) 7.9·10 3 N Bartol+RQPM  4·10 4 expected events/year N Okada  4·10 8 expected events/year Atmospheric neutrinos are generated according to the Bartol + RQPM (highest prediction) flux Atmospheric muons are generated according to the Okada parameterization, taking into account the depth of the NEMO Capo Passero site (3500 m) and the flux variation inside the detector sensitive height (~ 900 m): Astrophysical neutrinos: source declination:  = - 60˚ - 24 hours of diurnal visibility - large up-going angular range covered by the source (   24  – 84  ) Neutrino energy range:10 2 - 10 8 GeV

15. C.Distefano Barcelona July 4 – 7, 2006 LNS Sensitivity for a point-like (  = -60˚) neutrino source (3 years) Search bin: NEMO 0.5˚ IceCube 1˚  =2 IceCube sensitivity values from Ahrens et al. Astrop. Phys. 20 (2004) 507 Neutrino energy range: 10 2 - 10 8 GeV   (d  /d  ) 90 expressed in GeV  -1 /cm 2 s

16. C.Distefano Barcelona July 4 – 7, 2006 LNS Sensitivity for a point-like (  = -60˚) neutrino source (3 years) Detector sensitivity as a function of the high energy neutrino cut-off  max Hard spectrum sources: the detector sensitivity is better and gets better if the spectrum extends to VHE. Soft spectrum sources: the detector sensitivity doesn’t vary much with  max.

17. C.Distefano Barcelona July 4 – 7, 2006 LNS Sensitivity for a point-like neutrino source (3 years) =2=2 Diurnal visibility: Time per day spent by the source below the Astronomical Horizon with respect to the latitude of the Capo Passero site. The detector sensitivity gets worse with increasing declination due to the decrease of the diurnal visibility. Equatorial coordinates Detector sensitivity as a function of the source declination Average search bin: = 0.5°

18. C.DistefanoCRIS 2006 – Catania May 29 – June 2 LNS Microquasar: LS 5039 HESS observed TeV  -rays from LS 5039 Observed gamma-ray spectrum:   (  0.25 TeV) = 5.1  0.8·10 -12 ph/cm 2 s  = 2.12  0.15 Aharonian et al. astro-ph/0508658 Aharonian et al. Science 309, 746, 2005 Neutrino energy flux: f (  0.1 TeV) ~ 10 -10 erg/cm 2 s Sensitivity: f, 90 is expressed in erg/cm 2 s Selected events: N  s : source events; N  b : bkg events. Expected neutrino events in 3 years of data taking:

19. C.DistefanoCRIS 2006 – Catania May 29 – June 2 LNS SNR: RX J1713.7-3946 Aharonian et al. Nature 432, 75, 2004 Expected neutrino flux: Alvarez-Muñiz & Halzen (ApJ 576, L33, 2002): d  /d  ~ 4 ·10 -8  -2 cm -2 s -1 GeV -1  max = 10 TeV Costantini & Vissani (Astrop. Phys. 23, 477, 2005): d  /d  ~ 3 ·10 -8  -2.2 cm -2 s -1 GeV -1   = 50 GeV  1 PeV Expected neutrino events in 3 years of data taking: Sensitivity:   (d  /d  ) 90 is expressed in GeV  -1 /cm 2 s Selected events: N  s : source events; N  b : bkg events.

20. C.Distefano Barcelona July 4 – 7, 2006 LNS Outlook The NEMO project: R&D study for the realization of the Mediterranean km 3 neutrino telescope: Search, characterization and monitoring of an adequate deep sea site; Development of technologies for the km3 ; Test of prototypes in deep sea: NEMO Phase-1 in Catania; Realization of a marine infrastructure for the km3: NEMO Phase-2 in Capo Passero. Angular Resolution and Pointing Accuracy: Detection of the Moon shadow in 100 days; Estimated angular resolution 0.2°; Absolute pointing can be recovered looking at the Moon Shadow. Detector Sensitivity to point sources (3 years): NEMO (  =2,10 2 -10 8 GeV,  =-60°)1.2·10 -9 E -2 /(GeV cm 2 s)search-bin 0.5° ICECUBE 2.4·10 -9 search-bin 1° Discussed physics cases:  QSO LS 5039 and SNR RXJ1713.7-3946: both sources could be detected in 3 years; a survey of TeV gamma-ray sources is under analysis.

21. C.Distefano Barcelona July 4 – 7, 2006 LNS

22. C.Distefano Barcelona July 4 – 7, 2006 LNS Weighted Events Simulation of atmospheric neutrino background We use the ANTARES event generation code (weighted generation); We simulated a power law interacting neutrino spectrum: X=2 for 10 2 GeV <  < 10 8 GeV ; N gen = 7·10 9 interacting neutrinos 4  isotropic angular distribution The atmospheric neutrino events are weighted to the Bartol + RQPM (highest prediction) flux N rec  3.7·10 5 reconstructed events Bartol+RQPM 1 year N Bartol+RQPM  4·10 4 expected events/year Events at the detector

23. C.Distefano Barcelona July 4 – 7, 2006 LNS Simulation of atmospheric muon background The events are generated at the detector, applying a weighted generation technique. We simulate a broken power law spectrum (compromise between the requirement of high statistics and CPU time consumption): The atmospheric muon events are weighted to the Okada parameterization (Okada, 1994), taking into account the depth of the NEMO Capo Passero site and the flux variation inside the detector sensitive height (~ 900 m): X=1 for   < 1 TeV; N gen = 3·10 7 events X=3 for   > 1 TeV; N gen = 2.5·10 7 events N rec  3.8·10 6 reconstructed events N Okada  4·10 8 expected events/year t gen  4 days Weighted Events Okada 1 year Events at the detector Weighted Events Okada 1 year Events at the detector

24. C.Distefano Barcelona July 4 – 7, 2006 LNS Simulation of atmospheric muon background The events are generated at the detector, applying a weighted generation technique. We simulate a broken power law spectrum (compromise between the requirement of high statistics and CPU time consumption): The atmospheric muon events are weighted to the Klimushin, Bugaev & Sokalski parameterization (PRD, 64, 014016, 2001), taking into account the depth of the NEMO Capo Passero site and the flux variation inside the detector sensitive height (~ 900 m): X=1 for   < 1 TeV; N gen = 3·10 7 events X=3 for   > 1 TeV; N gen = 2.5·10 7 events N rec  3.8·10 6 reconstructed events N Okada  5·10 8 expected events/year t gen  4 days 1 year Events at the detector 1 year Events at the detector

25. C.Distefano Barcelona July 4 – 7, 2006 LNS Atmospheric muon background for a point-like source The statistics of generated events corresponds to a few days. Reconstructed events have a RA flat distribution. We can project the full sample of simulated events in a few degrees bin  RA, centered in the source position. We get statistics of atmospheric muons corresponding to a time of ~1 year for each microquasar. Distribution of equatorial coordinates of the reconstructed atmospheric muons. Weighted Counts

26. C.DistefanoCRIS 2006 – Catania May 29 – June 2 LNS =1=1 Event detection for a point-like (  = -60˚) neutrino source reconstruction selection Energy spectra of reconstructed and selected neutrino events (3 years) neutrino energy range 10 2 -10 8 GeV =2=2  =1.5  =2.5

27. C.Distefano Barcelona July 4 – 7, 2006 LNS Estimate of the detector angular resolution  = 0.19 ± 0.02 deg Event Selection: N hit min = 20  cut = -7.6 S 1year =5.5 median angle of selected events: estimated angular resolution:  = 0.22 deg Reconstructed Selected

28. C.Distefano Barcelona July 4 – 7, 2006 LNS Study of the telescope absolute pointing We introduce a rotation  around the Z axis to simulate a possible systematic error in the absolute azimuthal orientation of tracks. (1 year of data taking) for   0.2  (expected accuracy), the shadow is still observable at the Moon position; for   0.2  (pessimistic case), systematic errors may be corrected; the presence of possible systematic errors in the absolute zenithal orientation is still under analysis. Moon rest frame

29. C.Distefano Barcelona July 4 – 7, 2006 LNS The km3 telescope: a downward looking detector Neutrino telescopes search for muon tracks induced by neutrino interactions The downgoing atmospheric  flux overcomes by several orders of magnitude the expected  fluxes induced by interactions. On the other hand, muons cannot travel in rock or water more than  50 km at any energy Upgoing and horizontal muon tracks are neutrino signatures

30. C.Distefano Barcelona July 4 – 7, 2006 LNS Atmospheric muon background vs depth Downgoing muon background is strongly reduced as a function of detector installation depth. Depth >3000 m (  1 km rock) is suggested for detector installation NEMO NESTOR ANTARES AMANDA Bugaev BAIKAL

31. C.Distefano Barcelona July 4 – 7, 2006 LNS Cherenkov track reconstruction pseudo vertex ANTARES Cherenkov photons emitted by the muon track are correlated by the causality relation: The track can be reconstructed during offline analysis of space- time correlated PMT signals (hits). Fit yields muon track parameters ( ,   ) and number of hit PMTs

32. C.Distefano Barcelona July 4 – 7, 2006 LNS Event selection quality cut: The used reconstruction algorithm is a robust track fitting procedure based on a maximization likelihood method. The reconstruction may give more than one possible solutions: -  >  cut   - log(L)/N DOF +0.1(N comp -1) log(L)/N DOF  log-likelihood per degrees of freedom N comp  number of compatible solutions (within 1  ) energy cut: - N fit >N fit min N fit  number of hits in the reconstructed event angular cuts: - rejection of down-going tracks -  rec <  max  rec  reconstructed event direction - choice of the search bin size - r<r min r  angular distance from source position The optimal values of  cut, N fit min,  max and r min are chosen optimizing the detector sensitivity.

33. C.Distefano Barcelona July 4 – 7, 2006 LNS Sensitivity for a point-like (  = -60˚) neutrino source (3 years) Search bin: NEMO 0.5˚ IceCube 1˚  =2 IceCube sensitivity values from Ahrens et al. Astrop. Phys. 20 (2004) 507   (d  /d  ) 90 is expressed in GeV  -1 /cm 2 s Neutrino energy range:10 2 - 10 8 GeV

34. C.Distefano Barcelona July 4 – 7, 2006 LNS Sensitivity for a point-like neutrino source (3 years) =2=2 Diurnal visibility: Time per day spent by the source below the Astronomical Horizon with respect to the latitude of the Capo Passero site. The detector sensitivity gets worse with increasing declination due to the decrease of the diurnal visibility. Equatorial coordinates Detector sensitivity as a function of the source declination = -7.3 no selection in N fit  max = 90°-101° = 0.5°

35. C.Distefano Barcelona July 4 – 7, 2006 LNS Microquasar: LS 5039 HESS observed TeV  -rays from LS 5039   (  0.25 TeV) = 5.1  0.8·10 -12 ph/cm 2 s  = 2.12  0.15 Aharonian et al. astro-ph/0508658 Aharonian et al. Science 309, 746, 2005 f (  0.1 TeV) ~ 10 -10 erg/cm 2 s f, 90 is expressed in erg/cm 2 s Expected neutrino events in 3 years of data taking: N  s : source events; N  b : bkg events.

36. C.Distefano Barcelona July 4 – 7, 2006 LNS SNR: RX J1713.7-3946 Aharonian et al. Nature 432, 75, 2004 Expected neutrino flux: Alvarez-Muñiz & Halzen (ApJ 576, L33, 2002): d  /d  ~ 4 ·10 -8  -2 cm -2 s -1 GeV -1  max = 10 TeV Costantini & Vissani (Astrop. Phys. 23, 477, 2005): d  /d  ~ 3 ·10 -8  -2.2 cm -2 s -1 GeV -1   = 50 GeV  1 PeV   (d  /d  ) 90 is expressed in GeV  -1 /cm 2 s N  s : source events; N  b : bkg events. Expected neutrino events in 3 years of data taking: