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Combining Gamma and Neutrino Observations

This presentation discusses the capabilities of Neutrino Telescopes like AMANDA-II and ANTARES, their angular resolution, and potential sources including gamma-selected AGN classes. The concept of transient sources and the idea of combining neutrino and gamma observations are explored.

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Combining Gamma and Neutrino Observations

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  1. Combining Gamma and Neutrino Observations Christian Spiering, DESY

  2. Capabilities of Neutrino Telescopes • AMANDA-II, ANTARES class • Effective  area : 0.1 m² @ 10 TeV ~ 1 m² @ 100 TeV • Angular resolution AMANDA ~ 2.2° • Angular resolution ANTARES < 1° (Note: angle (,) ~ 1.5° @ 1 TeV, 0.5° @ 10 TeV ) • IceCube • Ama + 9 strings (2007 configuration): ~ 2-3  AMANDA sensitivity • full array (2011) ~ 30  AMANDA sensitivity • angular resolution 0.4-1.0° C. Spiering CTA Meeting Berlin May 4, 2006

  3. AMANDA Sky 2000-03 equatorial coordinates C. Spiering CTA Meeting Berlin May 4, 2006 3329 events

  4. Significance Map AMANDA 2000-2003 equatorial coordinates Highest significance: 3.4σ σ Compatible with statistical fluctuations of a smooth background of atmospheric neutrinos C. Spiering CTA Meeting Berlin May 4, 2006

  5. Reduce Trial Factor by Source Selection • Five TeV-Blazars • Seven GeV-Blazars • Eight Microquasars • Four SNRs • Six other selected objects • Three CR triplets TOTAL : 33 SOURCES C. Spiering CTA Meeting Berlin May 4, 2006

  6. Excess Probabilities 33 tested sources • Highest significance: CRAB • Compatible with statistical fluctuation • Adding year 2004 does not increase significance C. Spiering CTA Meeting Berlin May 4, 2006

  7. Source stacking of gamma-selected AGN classes No excess for any of the classes  upper limits C. Spiering CTA Meeting Berlin May 4, 2006

  8. Transient Sources • „Cluster Search“ Approach: Search for time clusters of events from directions of 12 sources which are known to flare • „Flare Search“ Approach: For 4 sources: search for coincidences of  events with observed high states of these sources  enhancement of signal/background C. Spiering CTA Meeting Berlin May 4, 2006 ~ 1 neutrino/(search bin  year)

  9. A Curious Coincidence Flux of TeV photons (arb. units) 3   2 1 0 2000 2001 2002 2003 Year May June July WHIPPLE Arrival time of neutrinos from the direction of ES1959+650 orphan flare C. Spiering CTA Meeting Berlin May 4, 2006

  10. Could that have been a „signal“ ? • We cannot judge significance since defini-tion a for flare was „TeV gamma + X-ray“  orphan flare realized only a posteriori • Exercise: • Assume a source with 1% flaring rate (The big unknown. Need long-term monitoring ! ) • 3 , one coinciding with a flare: P~0.03 • 3 , two coinciding with a flare: P~0.001 • 3 , three coinciding with a flare: P~0.00003 • (trial factor for multi-source analysis to be included) • 2 neutrinos would correspond to a flux ~ 50 times higher than most models predict. Some models allow higher fluxes! C. Spiering CTA Meeting Berlin May 4, 2006

  11. Could that have been a „signal“ ? We don't know, however ... C. Spiering CTA Meeting Berlin May 4, 2006

  12. This Coincidence Triggered Many Ideas and Questions • Need long-term monitoring in order to catch as many flares as possible • Observation of coincidence can boost the significance considerably • Significance is poorly quantifiable since the flaring rate is poorly known • Need long-term monitoring also in order to better quantify flaring rate C. Spiering CTA Meeting Berlin May 4, 2006

  13. More … • What do we call a flare ? (Threshold, duration,….) • What are typical flare lengths ? (this defines reasonable coincidence windows) • What is the relation between gamma and neutrino flux, and between typical gamma energies and neutrino energies ? • Can neutrino telescopes trigger Cherenkov telescopes (ToO, Target of opportunity trigger) ? C. Spiering CTA Meeting Berlin May 4, 2006

  14. Small, dedicated telescopes for long-term monitoring • Better understanding of long-term behaviour of the sources • Get a larger statistics for orphan flares • Benefit for neutrino  gamma flare coincidences: long-term monitoring of time variability @ TeV energies allows better calculation of significances of coincidences. • Background reduction w. r. t. neutrino observation • Northern Site vs. Southern Site ? • Distributed vs. Single Site ? C. Spiering CTA Meeting Berlin May 4, 2006

  15. Target of Opportunity Trigger : The Idea • Trigger gamma telescopes by neutrinos • Alternative trigger to X-ray trigger • Advantage: „Hadronic Trigger“ • Disadvantages: mostly atmospheric neutrinos (improves with angular resolution and, for hard spectra, energy threshold) C. Spiering CTA Meeting Berlin May 4, 2006

  16. Target of Opportunity Trigger: How might it work ? • Select a few sources with flary behaviour • Preferently, these sources should be those which the Gamma telescopes observe anyway from time to time • If IceCube (AMANDA) detects a neutrino from one of the selected sources, it generates an alert (within ~20 minutes) • A Gamma Telescope points to the source, if the source is in its FoV within, say, 24 h C. Spiering CTA Meeting Berlin May 4, 2006

  17. Target of Opportunity Trigger: Questions (1) • How many false triggers due to atmospheric  ? • AMANDA: search window 2-3°, ~2 atmospheric  in 365 days • IceCube: search window ~1°, ~6 atmospheric  in 365 days • For 5 selected sources and 30% probability that the Gamma telescope can point to the source within 24 h, this translates to 3 (AMANDA) and 9 (IceCube) „false“ observations per year. • IceCube: request 2 coincident  ? This reduces background essentially to zero, but signal efficiency is also decreasing. C. Spiering CTA Meeting Berlin May 4, 2006

  18. Target of Opportunity Trigger: Questions (2) • What are the signal expectations ? • How can neutrino telecopes avoid to violate their blindness criteria ? • Should we run a test with AMANDA ? • depends much on how we judge the ES1959 coincidence … • We should not create non-justified hopes • Good test for common campaigns, start to link communities C. Spiering CTA Meeting Berlin May 4, 2006

  19. Summary • Neutrinos would give strongest proof of hadronic contributions • Knowledge of gamma flux variations can considerably increase the significance of neutrino observations • Neutrino community would profit from long-term monitoring of selected, flaring sources • Possibility of ToO trigger under investigation • Initiate vigorous program on phenomenology of sources C. Spiering CTA Meeting Berlin May 4, 2006

  20. Backup slides C. Spiering CTA Meeting Berlin May 4, 2006

  21. Possible Scheme for a ToO Trigger C. Spiering CTA Meeting Berlin May 4, 2006

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