1. Rolling Search For a Cascade GRB Signal: 3 Year Results
Brennan Hughey
Baton Rouge Meeting
April 10th, 2006

2. Overview of Analysis BATSE
Motivation: Several AMANDA analyses have looked for neutrinos in coincidence with GRBs. Many GRBs missed by gamma-ray satellites, especially in era between BATSE and Swift. Additionally, some transient sources may not have coincident photon emission
Goal: to search for transients (specifically GRBs) in the period without relying on satellite coincidence
BATSE

3. Schematic of rolling search: New time window starts with every event

4. Procedure
Optimized for Prompt GRB neutrino emission: broken power law spectrum with 105 and 107 GeV breaks
Utilizes cascade rather than muon channel
Searches in time bins of both 1 second and 100 seconds after each surviving event

5. Data Reduction
High Energy Filter: cut on nhits and fraction of hit modules with >2 hits
Flarechecking cuts
First level cuts to restore exponential distributions
Extended flarechecking removes “flariest” 1% from stable variables
Cut on number of direct hits
Six variable Support Vector Machine Cut
Combination of topological and energy-related cuts
Similar to neural network
Many possible cut strengths
Black – surviving
Other colors –
Remove by
flarechecking
Black – real
Red – signal MC
Blue - Corsika

6. Optimization of Final Support Vector Machine Cut
Optimized for Discovery
Observable is largest single cluster of events in any time window during 3 year period – called Nlarge
Assumes stochastic (Poissonian) background
Short and long time windows optimized independently

7. Results 1 second search: 100 second search: Nlarge = 2. 70.14% chance
Results are very consistent with expectations based on background predictions

8. Doublets and Triplets:100 second search
| total |
| total
| 20

9. Number of doublets: 1 second search
| total
| 311
No doublets or triplets in either time window found to be in coincidence with a GRB from IPN lists.
Sample was unblinded again without flarechecking cuts, no significant fluctuations found in this case either.

10. Limit/Sensitivity Sensitivity determined using
- 90% CL Feldman Cousins likelihood ratio ordering method
- Primarily based on long time window, since long class has much greater fluence
- Poissonian Background with multiple periods per year
- Signal with relative per burst neutrino event rate distribution modeled by Guetta et al. (astro-ph/ )
Pre-systematics sensitivity/limit: 1.16 X 10-6 GeVcm-2s-1sr-1
(assumes 1:1:1 flavor ratio. See, however, Kashti & Waxman astro-ph/ )

11. Systematic Uncertainty
A preliminary treatment of systematics has been done,
but included parameters will require adjustment
Included uncertainties are:
30% for signal efficiency (estimate from other analyses)
20% for uncertainty in distribution of events per burst
10% for uncertainty in signal retention by cuts

12. More about Systematic Uncertainty
Limit is modified according to standard AMANDA procedure from:
- Cousins and Highland (Nuclear Instrumentation and Methods in Physics Research A320 (1992) )
- Conrad, Botner, Hallgren and Perez del Los Heros (hep-ex/ )
- Hill (physics/ )
Numerator in Likelihood Ratio is integrated over PDF of possible signal
efficiencies (currently taken as flat distributions)
Adjusted limit/sensitivity: X 10-6 GeVcm-2s-1sr-1 (from 1.16)

13. Choked Bursts
GRB jet may be unable to break through stellar envelope for very extended or slowly rotating stars
(Meszaros and Waxman astro-ph/ )
These choked bursts still have neutrino signal produced during propagation of jet within the star itself (equivalent to precursor neutrino emission, but not a precursor to anything)
Lower energy spectrum than analysis is optimized for
Analysis not sensitive to these, how far off depends on the choked burst event rate. It would be nice to have a detector that was a couple of orders of magnitude bigger.
1X GRBs – factor of ~1200
10X GRBs – factor of ~(number)
100X GRBs – factor of ~68

14. Outlook/Conclusions
Rolling search method provides a complementary procedure to satellite-coincident GRB searches
Sensitivity decreases due to lack of constraints, but competitive for periods without dedicated GRB satellites
Sampling from larger set of sources
Can be extended to muon channel
Erik Strahler has done preliminary work with Zeuthen point source cuts
Spatial as well as temporal scan
Cuts show less energy dependence, therefore less model dependence
Cascade channel could be re-optimized for other transients, probably not justified for AMANDA
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