1. Recent Results of Point Source Searches with the IceCube Neutrino Telescope Lake Louise Winter Institute 2009
Erik Strahler
University of Wisconsin-Madison
For the IceCube Collaboration
2/17/2009

2. Outline Motivation Astrophysical Neutrinos Detection Steady Sources
Transients
Outlook

3. Why look for Neutrinos?
Neutrinos from GRBs

4. The Cosmic Ray Connection
Sources of the highest energy cosmic rays are unknown. Need either very large B fields or spatial extent in order for acceleration mechanisms to work. GRBs are one of the few source candidates.

5. Astrophysical Neutrinos
Assume hadronic acceleration with equal energy injection as electrons
Protons interact with Syncrotron and IC photons
Typical energy spectrum: E-2

6. Neutrino Detection in IceCube
-Cherenkov radiation emitted by muon
-Optical sensors record arrival time of photons for track reconstruction

7. Detector IceTop 19 strings 677 optical modules Operated 2000-2007
Now integrated with IceCube 59
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8. Reconstruction
Tracks / Cascades reconstructed based on Cherenkov photon arrival times and intensities.
1.5 – 2.5 degrees. ~x2 in energy
.3-.4 in log(E) vs in log(E)
Better Pointing Resolution
Better Energy Resolution
Better Background Rejection

9. IceCube Analyses Cosmic Ray Composition Supernovae Neutrinos
Atmospheric Neutrinos
Indirect Dark Matter Searches
Diffuse Astrophysical Neutrinos
GZK Neutrinos
Time Integrated Point Sources
Transient Point Sources

10. Detection Challenges
Down-going muons from CR showers misreconstructed as up-going
Particularly coincident muons from independent showers
Must reject with tight quality cuts
Up-going atmospheric neutrinos from CR showers on other side of Earth
Softer energy spectrum than signal
Isotropically distributed
Downgoing Muons
Atmospheric
Neutrinos
Signal Neutrinos
Signal Neutrinos
Atmospheric
Neutrinos
Downgoing Muons

11. Shadow of the Moon
Important verification of timing and angular reconstruction
Structure can reveal anisotropies in resolution

12. Background PDF from data
Likelihood Method
Partial PDF:
Likelihood function:
Null hypothesis:
Likelihood Ratio:
Background PDF from data
Maximize LLH ratio by varying ns

13. Point Source Sensitivity

14. Point Source Results Hottest spot found at r.a. 153º , dec. 11º
preliminary
Hottest spot found at r.a. 153º , dec. 11º
est. nSrcEvents = est. gamma = 1.65
est. pre-trial p-value: -log10(p): (4.8 sigma)
Post-trials p-value of analysis is ~ 1.34% (2.2 sigma) ...

15. Fraction of Experiments Multiples of Predicted Flux
GRB Search
Fraction of Experiments
Multiples of Predicted Flux
Use measured quantities of all GRBs to model the neutrino emission
Discovery Potential: 2.6 * Prediction

16. GRB Result
Value of the likelihood ratio test is consistant with the null hypothesis
Preliminary Limit:
4.6 * Predicted Flux
Measured

17. UHE Point Source Sensitivity

18. UHE Point Source Results
preliminary
Coordinates: Dec. 1.00°, RA 103.5° (6.9 h)
Bin content: 8 events for 1.19 expected (109 in dec. band)
P-value: 2.9*10-5 (pre-trial prob.), post trial
equivalent sigma: (pre-trial), insignificant post-trial

19. Conclusions and Outlook
No astrophysical neutrinos yet, but sensitivities improving rapidly
40 string IceCube configuration online from April 2008
Already as large as full detector on long axis
Data run complete in April 2009
19 additional strings deployed this season.
Fermi Satellite adds significant observation opportunities for GRBs
80 string IceCube only a few years away. Expect factor 6-10 increase in sensitivity
Hopefully see signal neutrinos very soon!