Searches for point-like sources of cosmic neutrinos with the ANTARES telescope

Searches for point-like sources of cosmic neutrinos with the ANTARES

telescope

Giulia Illuminati on behalf of the ANTARES Collaboration X CPAN DAYS - 29/10/2018 – Salamanca

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Neutrino Astronomy

Neutrinos:

• electrically neutral -> trajectory not affected by magnetic fields, point back to the source

• stable -> travel long distances

• weakly interacting -> penetrate regions which are opaque to photons

𝑝 + 𝛾 → Δ^' → 𝜋^'+ 𝑛

𝜋^' → 𝜇^' + 𝜈_, → 𝑒^' + 𝜈_. + 𝜈̅_, + 𝜈_,

Ø Provide a strong indication of hadronic acceleration in astrophysical sources

𝜈_.: 𝜈_,: 𝜈₁ = 1: 2: 0 𝜈_.: 𝜈_,: 𝜈₁ = 1: 1: 1

at the source at Earth

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µ

Cherenkov angle in water θC~ 42°

• Cherenkov radiation

detected by arrays of PMTs

• Position, time and charge used to reconstruct

direction and energy

ɣ

ɣ

ν

ν

µ

νµ µ

N W X

key interaction (CC):

ν

+ N -> ℓ+ X

• Earth used as shield against up-going atmospheric muons

• Detector deployed in deep water/ice to reduce down-going atmospheric muons

• Low ν cross section requires large detector volumes

• Either CC or NC interaction with a nucleus inside or nearby the

detector volume

Neutrino telescopes:

Detection principle

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Global Neutrino Network (GNN)

o ANTARES and KM3NeT Mediterranean Sea o IceCube

Antarctic Ice o Baikal

Lake Baikal

~ 3.5π sr sky coverage

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The ANTARES neutrino telescope

~60 m 450 m

Junction boxes

Electro-optical cable

Buoy

o First detection line installed in early 2006 o Completed in 2008

o 2475 m depth in the Mediterranean Sea o 40 km offshore from Toulon

• Three-dimensional array of 885 PMTs

• 12 vertical lines, 25 storeys

• 3 PMTs per storey

• PMT facing 45° downwards

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Event topologies: TRACKS and SHOWERS

Track-like events:

ν_μ (ν_τ ) neutrino

CC interaction near the detector

è track

Angular resolution < 0.4° for E_ν > 10 TeV Angular resolution < 3°

Shower-like events:

all neutrinos NC

ν_e,ν_τCC interaction inside or very close to the

detector è shower

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ANTARES standard point-source search method

Maximum likelihood ratio approach

𝑆 7 = 𝑆 89:;. ⋅ 𝑆 .=.>?@

𝐵 7 = 𝐵 89:;. ⋅ 𝐵 .=.>?@

Signal PDFs:

Background PDFs:

δ

RA

E

Background

Signal

Source with E

spectrum assumed

𝐿 𝑛

, 𝛾, … = F F [ 𝑛

𝑁

𝑆

+ 1 − 𝑛

𝑁

𝐵

]

7∈H

H

𝑇𝑆 = −2 log 𝐿 𝑛

= 0

𝐿 𝑛Q

, 𝛾Q

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Recent searches for point-sources

1) Search for neutrinos from TXS 0506+056

1.1) Online search

1.2) Time integrated search 1.3) Time dependent search

2) Search for time and space correlation between ANTARES data and IceCube high-energy events

3) ANTARES-IceCube combined search for point-sources

1) TXS 0506+056

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• IceCube-170922A detected on 22 September, 2017

• ~290 TeV neutrino induced muon track

• High probability of being of astrophysical origin

• Coincident in direction and time with a gamma-ray flare from the blazar TXS 0506+056 (Fermi-LAT, MAGIC)

• 9.5 years of IceCube neutrino observations investigated to search for excess emission at the position of TXS 0506+05

• 3.5σ evidence for neutrino emission from the direction of the blazar between September 2014 and March 2015 found

Three different searches for neutrino candidates, associated with the IceCube-170922A event or from the direction of TXS 0506+056,

performed by the ANTARES Collaboration

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1.1) TXS 0506+056: Online search

Visibility map for the ANTARES detector of IC170922A (x) in equatorial coordinates

• Alert of extremely High Energy (EHE) track event

• Searches in the ANTARES online data stream for up- going muon neutrinos in a 3º cone centered on the IceCube event coordinates in two time-windows centered on the event time:

• ±1 h

• ±1 day (46% visibility probability)

• No coincident up-going muon neutrino recorded

• 90% C.L. fluence upper limit for a ^RS_RT ∝ 𝐸^WX source:

Spectrum 90% C.L. Fluence^U.L. [GeV cm−2] 5%-95%

energy range

E^-2.0 15 3.3 TeV – 3.4 PeV

E^-2.5 34 450 GeV – 280 TeV

(RA, δ) = (77.43º, 5.72º) 14.2º below the horizon

1.2) TXS 0506+056: Time integrated search

Standard fixed source analysis applied to the 2007-2017 ANTARES data (livetime: 3136 days)

• Best fitted # of signal events 𝜇

= 1.03

• 3.4% pre-trial p-value

• 90% C.L. flux upper limits on the flux:

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Events close to TXS 0506+056 in the ANTARES data:

13 track-like and1shower-like candidates within 5º

Spectrum _Φ

Z[[TeV

\[% [10^{WZ^} GeV−1cm−2s−1]

E^-2.0 1.6

E^-2.3 1.4

E^-2.5 1.0

Closest event at 0.3º from the source position Recorded on December 12, 2013 Only 9% of ν events have higher estimated energy

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1.3) TXS 0506+056: Time dependent search

P𝐷𝐹 = 𝑃

⋅ 𝑃

⋅ 𝑃

t₀ t σ t₀ = MJD 57004 σ = 55 days

Δt = 550 flaring days (±5σ)

t Background time PDF estimated from data

Gaussian flare

t

Box flare

t_start t_end

t_start= MJD 56937.81 t_end = MJD 57096.21 Δt = 158.40 flaring days

𝐿 𝑛

= F F [ 𝑛

𝑁

𝑆

+ 1 − 𝑛

𝑁

𝐵

]

7∈H H

• ANTARES time dependent search method

• Two signal time profiles provided by the IceCube Coll.

• Gaussian flare (centered on December 13, 2014)

• Box flare (centered on December 26, 2014)

• No signal found during either of the considered flares

• 90% C.L. upper limits on the neutrino flux:

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Spectrum 𝛷_Z[[^\[%TeV [10^{WZ^} GeV−1cm−2s−1]

E^-2.0 4.6

E^-2.1 4.4

E^-2.2 4.2

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2) Time correlation with IceCube events

t_obs day σ

σ= flare duration t_obs= source

observation time

P𝐷𝐹 = 𝑃

⋅ 𝑃

⋅ 𝑃

E

Background Signal

δ

RA

Maximum likelihood method

Four free parameters:

• number of signal events

• signal spectral index

• flare duration

• source position

Candidates:

54 IceCube high energy neutrino events ANTARES data sample:

6310 tracks 147 cascades

(days) σt

−1

10 1 10 10²

) σ(50%@5s n

0 2 4 6 8 10 12 14 16

Time dependent analysis, E-2.5

Time integrated analysis, E-2.5

Time dependent analysis, E-2.0

Time integrated analysis, E-2.0

PRELIMINARY

PRELIMINARY

log𝐿

= g g log 𝜇

𝑆

+ 𝑁

𝐵

− 𝜇

7∈H H

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sinδ

1

− −0.8 −0.6 −0.4 −0.2 0 0.2 0.4 0.6 0.8 1

]-2 Fluence [Gev cm

1 10 102

103

S(E) = E-2.0

Limits Sensitivity

S(E) = E-2.0

γ

2 2.1 2.2 2.3 2.4 2.5

,ICν90 N

0 0.5 1 1.5 2 2.5 3 3.5 4

EHE27 HESE45

sinδ

1

− −0.8 −0.6 −0.4 −0.2 0 0.2 0.4 0.6 0.8 1

]-2 Fluence [Gev cm

1 10 102

103

S(E) = E-2.5

Limits Sensitivity

S(E) = E-2.5

𝑁_hi^\[% = j Φ_[,X^kl ×𝐴_.oo^hi ×𝐸^WX𝑑𝐸

PRELIMINARY PRELIMINARY

PRELIMINARY

No correlation with IceCube events observed.

90% C.L. upper limits on fluence:

90% C.L. upper limit on the number of signal events expected to be observed by IceCube

2) Time correlation with IceCube events

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3) ANTARES-IceCube combined analysis

Complementarity for the Southern sky:

• Size

• Geographical location

• Atmospheric muon background

~60 m 450 m

Junction boxes

Electro-optical cable

Buoy

[TeV]

Eν 1

10− 1 10 10² 10³ 10⁴

]2 [meffA

3

10− 2

10− 1

10−

1 10 102

103

Graph

ANTARES IceCube

Graph

Effective Area Data sample:

• 9 years of ANTARES data (tracks and showers)

• 7 years of IceCube data (through-going tracks)

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3) ANTARES-IceCube combined analysis

sinδ

−1 −0.8 −0.6 −0.4 −0.2 0

] -1 s-2 [GeV cmν/dEΦ dν2 E

−9

10

−8

10

−7

10

= 2.0 90% C.L. Sensitivity for γ

IceCube 7 years ANTARES 9 years IceCube+ANTARES

= 2.0 90% C.L. Sensitivity for γ

sinδ

−1 −0.8 −0.6 −0.4 −0.2 0

] -1 s-2 [GeV cmν/dEΦ dν2 E

7

10− 6

10−

−5

10

= 2.5 90% C.L. Sensitivity for γ

IceCube 7 years ANTARES 9 years IceCube+ANTARES

= 2.5 90% C.L. Sensitivity for γ

90% C.L. sensitivity for different energy source spectra

∝ 𝐸

PRELIMINARY PRELIMINARY

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Conclusions

Ø Neutrinos are expected to provide complementary information to gamma-rays and protons of the high-energy universe

Ø IceCube has shown the first evidence for high-energy astrophysical neutrinos from a diffuse isotropic flux and the first association with a point-source

Ø Three different searches for neutrino candidates in the ANTARES data promptly triggered by the detection of IC170922A and the subsequent potential association with TXS 0506+56

Ø Time correlation analysis performed to possibly constrain the origin of the IceCube astrophysical diffuse signal from transient sources

Ø No significant evidence of cosmic neutrino sources found

Ø Most sensitive limits for a large fraction of the Southern Sky set, especially at neutrino energies below 100 TeV, expected to be significantly improved by combining ANTARES and IceCube data

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Backup

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Neutrino candidates registered by the ANTARES detector within an angular distance ∆Ψ from TXS 0506+056.

2) Time integrated search for neutrinos from

TXS 0506+056