Rolling Search For a GRB Cascade Signal

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Rolling Search For a GRB Cascade Signal

• Brennan Hughey
• March 19, 2005

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Our Story so far

• 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
• Background rejection is accomplished in 3 steps
• The high energy filter is applied cuts on nhits
  and OMs with gt 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

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Two Searches

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

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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.

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

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

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Poissonian Distribution of Events
Chi2 test yields a result of 76 for both plots.
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Poissonian Distribution of Events
Chi2 test yields a result of 75 for left plot
and 86 for right plot.
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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 gt 5 of the time, so this is a little
on the high side, but not a statistically
significant fluctuation
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Cascade Effective Volume

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

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Neutrino Effective Area
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Expected Distribution of Detected Signal Energies
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Comparison Between my Searchand
Satellite-Coincident Searches

• Disadvantage
• Requires multiple events for a detection.
• This means far lower likelihood of getting lucky
  from a faint source 1X10-4 events fluctuates to
  1 way more often than 3, so requires a
  particularly bright event even more than other
  analyses
• Limit on Waxman-Bahcall style flux from 667
  equivalent sources only 7X10-6 Gev/cm2 s sr
• (This will look better if a more realistic
  distribution of fluences is used)

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Comparison Between my Searchand
Satellite-Coincident Searches

• Advantages
• Can pick up GRBs missed by satellites
  -particularly useful given that CGRO went down in
  early 2000
• Can detect ?-ray dark choked bursts as described
  in 2001 Meszaros and Waxman paper
  astro-ph/0103275.
• Choked bursts would produce ? as normal GRBs
  but photons would fail to escape. Frequency
  unknown but could be as high as 100 times
  conventional GRB rate.
• Utilizes cascade channel and therefore searches
  all sky rather than 2p (okay, Ignacios analysis
  can do this too)

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Sphere of Sensitivity

• Starting with a GRB at redshift of z1
• 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 Eb? increases as 1/(1z)2.

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Sphere of Sensitivity long bursts
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Sphere of Sensitivity short bursts
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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 100 second search cuts
• Probability of 2 background events during burst
  times 0.01.
• Probability of 3 background events during burst
  times 5X10-4.

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Coincidences With Other Experiments MILAGRO

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

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Backup Slide cuts
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Backup Slide
50 TeV 43.43
100 TeV 48.99
300 TeV 56.24
700 TeV 61.01
1100 TeV 64.08

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Backup Slide cuts
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Backup Slide cuts
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Backup Slide ndird cut