Transcript Document

Neutrino Point Source Search Strategies
for AMANDA-II and Results from 2005
J. Braun, A. Karle, T. Montaruli
For the IceCube
Collaboration
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
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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
Gaussian
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as a 2D
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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:
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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
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Sensitivity
90% confidence level sensitivity to E-2 spectra
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Results for 2005
• 1.8 billion raw events recorded in
2005
• 6001 events survive quality cuts, 887
above d = 10o
• Search in range -5o < d < 82o
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2005 All-Sky Results
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
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Results for Candidate Sources
• The method is applied separately to a list of 26 candidate
sources to enhance discovery potential
P-value
m90
38.2
~1
5.9
253.5
39.8
0.184
18.1
Cyg. X-1
299.6
35.2
0.414
12.9
Cyg. X-3
308.1
41.0
0.458
11.0
NGC 1275
50.0
41.5
0.064
22.4
Crab
83.6
22.0
~1
9.24
MGRO J2109+37
304.8
36.8
0.152
20.1
Object
RAo
Dec.
Mrk 421
166.1
Mrk 501
o
E2F < m90.10-11 TeV cm-2 s-1
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• 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
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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.
8 E-2 Signal Events
• Minimization of  log(L)
with respect to signal
strength and spectral index
yields an estimate of both
parameters
• Approximate  2 log(L / Lˆ )
as a c2 distribution with
two degrees of freedom
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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.
50 E-2 Signal Events
• Minimization of  log(L)
with respect to signal
strength and spectral index
yields an estimate of both
parameters
• Approximate  2 log(L / Lˆ )
as a c2 distribution with
two degrees of freedom
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Benefit of Likelihood Method
• 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
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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
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