Neutrino Point Source Search Strategies for AMANDA-II: Results & Strategies

1. Neutrino Point Source Search Strategies for AMANDA-II and Results from 2005 J. Braun, A. Karle, T. Montaruli For the IceCube Collaboration

2. Motivation • No extraterrestrial high energy neutrino source yet observed • Need larger detectors and more sophisticated analysis methods • Current searches: Use event direction (time) • Construct a search to fully utilize • Event energy estimation • Event direction • Detector angular resolution

3. Method • Energy correlated observable: Number of hit channels • For each event at position xi, assign a probability of belonging to a source at xo with spectral index g • Model the detector point spread function as a 2D Gaussian

4. Method • A ±5o declination band centered on the source location contains N total events and is modeled as a mixture of signal and background in a likelihood function: • The Background PDF Bi depends on • Minimize –log(L) with respect to number of signal events and spectral index • Significance is measured by the ratio of best likelihood and background-only likelihood:

5. Discovery Potential 35% less events required for 5s detection at d = 42.5o 90% Chance of Discovery 90% of sources with the given E-2 flux are detected at 5s (3s) significance

6. Sensitivity 90% confidence level sensitivity to E-2 spectra

7. 1.8 billion raw events recorded in 2005 6001 events survive quality cuts, 887 above d = 10o Search in range -5o < d < 82o Results for 2005

8. Largest Excess: 3.6s d=48o , a=2.75h Log10(p-value) 69 out of 100 sky maps randomized in RA contain an excess of at least 3.6s 2005 All-Sky Results

9. Results for Candidate Sources • The method is applied separately to a list of 26 candidate sources to enhance discovery potential • No striking excesses found • Most significant source is NGC 1275 (Perseus A), p = 0.064 • 3 events near source location (~1.5 expected) • 80% chance of randomly observing this significance from a source on the list E2F < m90.10-11 TeV cm-2 s-1

10. What if a Source is Observed? • Suppose Markarian 421 produces 8 signal events in AMANDA following an E-2 spectrum and the background is well described by atmospheric neutrinos • >50% probability of 5s detection, assuming no trial penalty. • Minimization of with respect to signal strength and spectral index yields an estimate of both parameters • Approximate as a c2 distribution with two degrees of freedom 8 E-2 Signal Events

11. What if a Source is Observed? • Suppose Markarian 421 produces 8 signal events in AMANDA following an E-2 spectrum and the background is well described by atmospheric neutrinos • >50% probability of 5s detection, assuming no trial penalty. • Minimization of with respect to signal strength and spectral index yields an estimate of both parameters • Approximate as a c2 distribution with two degrees of freedom 50 E-2 Signal Events

12. Other benefits: Position confidence contours can be drawn similarly using information from the likelihood function Data from detectors with different angular resolution can be combined more efficiently Benefit of Likelihood Method

13. Conclusions • New methods enhance point source sensitivity and discovery potential by 30% • Adding an energy correlated observable additionally allows estimation of signal spectral index in the case of discovery • No significant excess observed in 2005