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Constraints to a Galactic component of the IceCube cosmic neutrino flux

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1Visioconference 4/9/2014

Maurizio Spurio

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Starting motivation

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Comparison between Aeff

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3• Different selection criteria • IceCube = 4p, high energy sample (En>30 TeV), almost bck free

• ANTARES= nm only, southern sky, lower energy

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Details: see

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The IceCube HESE

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From IceCube

arXiv:1405.5303

• It is possible, using the effective area, to obtain the normalization factor FD,G for any other spectral index G.

• We computed the values of FD, G for G from 2.0 to 2.5• This extend the possible range of astrophysical models for the

signal• In particular, we are interested on a possible Galactic component

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The normalization factors • Valid for a generic E-G spectrum• Derived from the IC effective areas

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A galactic component in HESE• A Galactic component is quoted statistically non-signicant by

the IceCube collaboration;• The expected signal from the Northern hemisphere (purely

extragalactic) is a factor of 2 larger than measured; • Assuming 3.6 Up and symmetric extragalactic contribution, the

expected Down HESE of extragalactic origin are: =6.2 (5.8) events for the E-2.0 (E-2.5) spectrum.

• Galactic contribution= 13.7-6.2 7.5 events

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I) A point-like Galactic source

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• Signal due to a point like source• np events out NIC are due to this

source, with energy spectrum:

• The normalization factor depends on the diffuse normalization factor (for G=2.0 , that reported in the IceCube paper)

The normalization factor can be derived with the use of the Aeff (E)

Same formula in:

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ANTARES has upper bounds

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For different energy spectra E-G:

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Results

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• The ANTARES 90% C.L. upper limit excludes that a single point-like source produces more than 5 IceCube events, assuming a spectral index G=2.0.

• A single point-like source yielding a cluster of more than 2 events is excluded for G=2.3

• A clusters made of two or more events is excluded for G> 2.3.

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II) Enhanced diffuse Galactic source

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• Signal due to a extended source, comparable with the IC angular resolution

• Size DW much larger than the ANTARES angular resolution

• nDW events out NIC are due to this source, with energy spectrum:

DW

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Predictions (nDW, DW) vs. G

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ANTARES bounds?• At present, missing constraints;• Problem: for an extended source, large background of

atmospheric neutrinos (50 events in a 8° radius); • Strategy: suppress the atmospheric neutrinos using the muon

estimated energy• Method already used in the FB analysis• Sensitivity:

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Perspectives

• It assumes the same optimization as for the FB analysis for any spectral index G;

• Signal/noise improves when the search solid angle decreases

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8°

20°

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Conclusions• The galactic component in the HESE sample is quantitatively

estimated (it could be over-fluctuation…)• Due to the similarity on the IC/ANTARES effective areas, a

point-like signal or an enhanced diffuse signal in the Galaxy can be seen/excluded by ANTARES

• 1) Source association (Padovani/Resconi style). See considerations in the Antoine talk

• 2) Presence of a point-like source. Upper limits already published by ANTARES constrain severly some hypothesis, in particular for energy spectra E-G with G>2.2

• 3) Extended source, seen as an enhanced diffuse flux.• Redo an analysis similar to that of the FB centered on the IC hot

spot and with windows 0.06 sr (8°) and 0.38 sr (20°)

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What about the safe «two orders on magnitudes»?• The statement is (in my opinion) a signal of the habit to

understimate ANTARES (a factor of 40 in effective volume…);• The crucial point to a possible verification/falsification of the

IC signal by ANTARES is the presence of a Galactic component• The statement on JHEA is due to an error in the formula for

the computation of the directional flux in Table 3 (DW=0.06 sr) and Table 4 (DW=0.38 sr) :

• which is incorrect by a factor of • = 209 for Table 3 • = 33 for Table 4

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Lets observe a signal, if a real Galactic component is present in the HESE sample

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