1. IC22 Unbinned GRB Search Utrecht Collaboration Meeting
Erik Strahler
UW-Madison
16/9/2008

2. IC22 Data Sample 43/44 Northern hemisphere quality bursts
Filtered to L3
Use complete year for background rejection
Yields good statistics (~77M events)
Bursts windows taken from the Swift T100s
Conservative
Easier than trying to figure out T90 information + padding
Total ontime: s
Blind runs containing GRB triggers

3. Simulation Corsika Dataset: 645 (0.3 days)
Corsika Coincident Dataset: 861 (0.71 days)
Neutrino-Generator Datasets:
651 (E − 1, 1M)
768 (E − 2, 5.5M)
Processed identically to data
Weighted to average WB prompt emission spectrum
Flux Normalization: 4.5E-9 GeV s-1 sr-1 cm-2
To Do: look at more muon statistics for checking tails

4. Cut Parameters

5. Bayesian Ratio
Reduced LLH vs. Ndir
Split
Reco
MinZen

6. L4 = L3 + paraboloid fit succeeded AND split reco succeeded AND neutrinos >= 90 degrees

8. “Loose” Cuts Pbf_status == 0 @ paraboloid error <5
Split reco minimum zenith angle >70 degrees
Bayesian likelihood ratio > 20
32 iter. Pandel reduced log-likelihood < 8.25
Umbrella reduced log-likelihood < 15

9. Efficiency vs. Energy
~50% at 100 TeV
(peak of WB signal acceptance)

10. Efficiency vs. NCH

11. Effective Area

12. Effective Area

13. Bayesian ratio > 20, rllh < 8.25

14. Likelihood Method Signal Spatial PDF signal
Similar Method to GRB080319B except with 43 stacked sources
Also incorporates energy as in the point source work
Currently using fixed E-2 signal. (WB makes little change)
Doesn’t make sense to fit the spectrum for 43 bursts and only 1 or 2 events
Perform algorithm while optimizing rllh and bayesian ratio
Signal Spatial PDF
x PDFiE
signal
atm.
corsika
signal

15. Test Statistic
0 injected signal

16. Optimized Cuts 3s, P=0.5 MDP optimization 4s, P=0.5 MDP optimization
Reduced LLH
Bayesian LLH Ratio
Reduced LLH
Bayesian LLH Ratio

17. Discovery Potential
Energy does not help as much as in the point source search
~15% improvement at P=0.5 for 4s

18. Conclusions Good event selection
Similar to point source search
Nearly at atm. neutrino level
Good signal retention (0.7 events expected)
Implemented likelihood function incorporating position, time, and energy (as nch)
Initial tests show good discovery potential
To Do:
Data stabililty
Run statistics for 5s numbers
Implement individual GRB flux expectations