# Presentation: 855217

## Rolling Search For a GRB Cascade Signal

- Brennan Hughey
- March 23, 2005

## Our Story So Far...

- Time

- The Rolling cascade search scans the entire data sample (year 2001) for a significant clustering of events above background

- The signal MC spectrum is e-produced cascades from a Waxman-Bahcall
- (Band function) spectrum with break energies at 7.7 X 104 and 1.0 X 107 GeV

## Our Story so far......

- Background rejection is accomplished in 3 steps:
- The high energy filter is applied – cuts on nhits and OMs with > 2 hits
- Ndird(muon fit)/nhits – a loose cut is applied on this parameter
- 6 variable svm cut – a support vector machine (which functions in a manner
- 	similar to a neural network) is used for further reduction
- Total background rejection ~106

## Run Selection

- Criteria:
- Long period of stable running (~30000 seconds)
- Period when station was open excluded
- “Special” runs excluded
- Nch distribution appears normal
- List checked against runs used in
- Zeuthen Point Source sample
- Time for search totals 233 days
- 186.4 days accounting for overall 80% livetime

## Two Searches

- BATSE experiment finds two classes of bursts, so we have two searches:
-         1 second and 100 seconds

## Support Vector Machine Selection

- SVMs were chosen such that the total chance of getting a false detection was less than 1% for both searches in the whole analysis – p value of .01 in the event of a detection – 1 second search svm retains 80% of signal and requires 3 events for significance. 100 second search svm retains 53% of signal and requires 4 events for significance.

- keep

- keep

- ___ - signal Monte Carlo _____ - real data  _ _ _ _  - background MC (dCorsika)

## Background rates

- Number of surviving events are shown as a function of run number

## Poissonian Distribution of Events

- Chi2 test yields a result of 76% for both plots.

## Poissonian Distribution of Events

- Chi2 test yields a result of 75% for left plot and 86% for right plot.

## Check - Bins With 2 Events

- Occurrence of bins with 2 events is not significant, but provides a useful check.
- Real data is compared to distribution produced by a Toy Monte Carlo
- 18 or more bins with 2 events will occur > 5% of the time, so this is a little on the
- high side, but not a statistically significant fluctuation

## Cascade Effective Volume

- Use of uncontained events allows effective volume greater than detector size (but means no directional reconstruction)

## Neutrino Effective Area

## Expected Distribution of Detected Signal Energies

## Comparison Between my Searchand Satellite-Coincident Searches

- Advantages:
- Can pick up GRBs missed by satellites -particularly useful given that CGRO went down in early 2000
- Can detect γ-ray dark choked bursts as described in 2001 Meszaros and Waxman paper: astro-ph/0103275.
-     Choked bursts would produce ν  as normal GRBs but photons would fail to escape.  Frequency unknown but could be as high as ~100 times conventional GRB rate.
- Approach that hasn’t been tried – always a chance of finding something new
- Utilizes cascade channel and therefore searches all sky rather than 2π  (okay, Ignacio’s analysis can do this too)

## Comparison Between my Searchand Satellite-Coincident Searches

- Disadvantage
- 	Lack of space and time restraints makes
- 	background rejection much more difficult:
- 	Requires multiple events for a detection.
-    Large negative impact on sensitivity and reduces chance of a chance fluctuation from an ensemble of weak sources

## Sensitivity Estimate

- Assuming ensemble of 667 identical bursts - 425 in livetime

- Application slightly non-standard since we
- count “clusters” rather than individual events

- Sensitivity estimate:  1 X 10-5 GeV/cm2 s sr
- Results checked by calculating flux such that there is a 90%
- chance of seeing a signal from one burst – almost identical result
- Depressing result, but should improve if one applies a more
- realistic model of burst strengths, i.e. model based on distribution
- in Guetta et al.  Work is in progress on this...

## Sphere of Sensitivity

- Starting with a GRB at redshift of z=1
- Bring closer: 2 effects happen
- Geometric effect: Fluence at Earth proportional to 1/r2
-     This makes a huge difference in the expected event  rate.
- Relativistic effect: Spectrum changes shape as it moves closer: Ebν increases as 1/(1+z)2.

## Sphere of Sensitivity: long bursts

## Sphere of Sensitivity: short bursts

## Coincidences With Other Experiments: IPN3

- With framework already in place, a check for temporal coincidence with satellite detections is fairly straightforward
- 81 bursts during livetime from IPN3 catalogs time estimates obtained mostly from Konus-Wind lightcurves
- For slightly tightened search cuts:
*Preliminary* sensitivity estimate based on assumption of 667 equivalent bursts:  8.6 X 10-7 GeV/cm2 s sr with an on-time background of 0.1 events
- Probability of 2 background events during burst times: 0.0046.
- Probability of 3 background events during burst times: 1.5X10-4.

## Coincidences With Other Experiments: MILAGRO

- I will also be collaborating with the MILAGRO air shower array on AMANDA-MILAGRO coincidence studies

## Backup Slide: cuts

## Backup Slide: cuts

## Backup Slide: cuts

## Backup Slide

| 50 TeV | 43.43% |
| --- | --- |
| 100 TeV | 48.99% |
| 300 TeV | 56.24% |
| 700 TeV | 61.01% |
| 1100 TeV | 64.08% |

## Backup Slide: Tea vs. ANIS

## Backup Slide: ndird cut