Point-like Source Searches with the ANTARES and KM3NeT Neutrino Telescopes

Point-like Source Searches

with the ANTARES and KM3NeT Neutrino Telescopes

Giulia Illuminati on behalf of the ANTARES and KM3NeT Collaborations IX CPAN DAYS - 23/10/2017 – Santander

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Outline

o Neutrino Astronomy o Neutrino telescopes

• Detection Principle

• Operating Neutrino Telescopes v ANTARES

v KM3NeT

• Event Topologies

o ANTARES point-like source analysis

• Data sample

• Analysis Method

• Results

o ANTARES on-going analyses

• ANTARES-IceCube combined analysis

• ANTARES time correlation analysis with IceCube events

o Expectations for KM3NeT

Neutrino Astronomy

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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

o Cosmic rays and photons current main cosmic messengers o CRs deflected by magnetic fields

o Photons absorbed by dense regions

𝑝 + 𝛾 → Δ^' → 𝜋^'+ 𝑛

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

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

at the source at Earth

Ø Produced in astrophysical sources where hadrons are accelerated Ø Provide a strong indication of

hadronic acceleration

𝑝 + 𝛾 → Δ^' → 𝜋⁶+ 𝑝 𝜋⁶ → 𝛾𝛾 𝑛 → 𝜋⁷+ 𝑝

𝜋⁷ → 𝜇⁷ + 𝜈̅_, → 𝑒⁷+ 𝜈̅_.+ 𝜈̅_, + 𝜈_,

ν

ν

µ

Neutrino telescopes:

Detection principle

νµ µ

N W X

key interaction:

ν

+ N -> ℓ+ X

µ

Cherenkov angle in water θC~ 42°

• Cherenkov radiation

detected by arrays of PMTs

• Position, time and charge used to reconstruct

direction and energy

• 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

ɣ

ɣ

Neutrino telescopes

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o ANTARES and KM3NeT Mediterranean Sea

o IceCube

Antartic Ice o Baikal

Lake Baikal

~ 3.5π sr sky coverage

The European neutrino telescopes:

ANTARES

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~60 m 450 m

Junction boxes

Electro-optical cable

Buoy

o Largest neutrino telescope in the Northern Hemisphere 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

The European neutrino telescopes:

KM3NeT

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KM3NeT/ARCA 36°16’ N 16°06’ E

KM3NeT/ARCA

o Under construction

o 3500 m depth in the Mediterranean Sea

o 100 km offshore from Porto Palo di Capo Passero, Sicily o 2 sparse building blocks

o 1-10 TeV energy threshold

o High-energy neutrino astronomy

KM3NeT/ORCA 42° 48’ N 06° 02’ E

KM3NeT/ORCA

o Under construction

o 2450 m depth in the Mediterranean Sea o 40 km offshore from Toulon

o 1 dense building block o GeV energies

o Oscillations, mass hierarchy

ORCA 9 m ARCA 36 m

~210 m ORCA

~1 km ARCA

3 building blocks

115 strings per building block 18 optical modules per string 31 PMTs per OM

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Event topologies - TRACKS

Track-like events:

ν_μ (ν_τ ) neutrino

CC interaction near the detector è track

ANTARES

Angular resolution < 0.4° for E_ν > 10 TeV Angular resolution < 0.1° for E_ν> 100 TeV

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Event topologies - SHOWERS

Shower-like events:

all neutrinos NC

νe,ν_τCC interaction inside or very close to the

detector è shower

ANTARES

Angular resolution < 3° Angular resolution < 1.5°

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ANTARES all-flavour neutrino point source analysis:

Data sample

sinδ

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

s)2 cm-1 GeV8 /(10S A

0 0.5 1 1.5 2 2.5 3 3.5 4

Tracks Showers x 3

PRELIMINARY

Acceptance as a function of the source declination for a E^-2 energy spectrum.

o Jan 29, 2007 to Dec 31, 2015 o 2423.6 days of lifetime

o Track and Shower events

o 7622 tracks and 180 showers

ANTARES all-flavour neutrino point source analysis:

Search method: likelihood

𝑆 9 = 𝑆 :;<=. ⋅ 𝑆 .?.@AB

𝐵 9 = 𝐵 :;<=. ⋅ 𝐵 .?.@AB

Signal PDFs

Background PDFs

log𝐿 :'H = I I log 𝜇 :9A J 𝑆 9 J + 𝑁 J 𝐵 9 J − 𝜇 :9A

9∈J J

δ

RA ^{−1 −0.8 −0.6 −0.4 −0.2 0 0.2 0.4 0.6} _sin(^0.8 _δtr)¹

Selected track events

0 100 200 300 400 500 600 700 800

PRELIMINARY

E

Background Signal

𝑄 = log𝐿

− log𝐿

Test Statistic

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Source with E^-2 spectrum assumed

ANTARES all-flavour neutrino point source analysis:

Search method: strategies

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o Full-sky search

• TS evaluated in squares of 1°x1° over the ANTARES visible sky

o Galactic Centre region search

• TS evaluated in squares of 1°x1° over a restricted region around the GC:

ellipse, 15° semi-axis in galactic latitude, 20° semi-axis in galactic longitude

[1] arXiv:1405.5303

[2] PoS ICRC2015 (2016) 1081

Free parameters:

Ø 𝜇

Ø 𝜇

Ø 𝛼

Ø 𝛿

o Candidate list searches

• 106 known astrophysical objects (Pulsars, SNRs, …)

• 13 IceCube tracks from the HESE sample [1][2]

o Sagittarius A* location

• Tested as an extended source by assuming a Gaussian emission profile of various widths

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ANTARES Results: Sensitivities and Limits

Full-sky and Candidate list searches

Sensitivities and upper limits at a 90% C.L. on the signal flux from the Full-sky and the Candidate list searches

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ANTARES Results: Sensitivities and Limits

Galactic Centre region search

sinδ

−0.7 −0.6 −0.5 −0.4 −0.3 −0.2 ]-1 s-2 [TeV cm90%CL Φ2 E

16 18 20 22 24 26 28

30×10⁻¹²

= 2.0° σ

° = 1.0 σ

= 0.5° σ

= 0.0° σ

PRELIMINARY

sinδ

−0.7 −0.6 −0.5 −0.4 −0.3 −0.2

]-1 s-2 cm-1γ [TeV090%CL Φγ E

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10−

−10

10

= 2.5 γ

= 2.3 γ

= 2.1 γ

= 2.0 γ

PRELIMINARY

90% C.L. upper limits of the search restricted to the region around the origin of the galactic coordinates at (α,δ) = (266.40°,-28.94°) assuming different spectral indices for the neutrino flux (left) and different

source extensions for ɣ= 2 (right).

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ANTARES Results: Sensitivities and Limits

Sagittarius A*

°] σ [

0 1 2 3 4 5 6

]-1 s-2 [TeV cm90%CL Φ2 E 11−10

−10

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Sensitivity (assuming width) Sensitivity (assuming point-source) 90% C.L. Limit

discovery flux (assuming width) 5σ

discovery flux (assuming point-source) 5σ

PRELIMINARY

Discovery flux (solid red), median sensitivity (dotted blue) and upper limits (solid blue) at 90% C.L. for a search for an extended source at Sagittarius A* at (α,δ) = (266.42°,-29.01°)

assuming different angular extensions σ. The dashed lines correspond to the point-like source assumption.

o Exploit the complementarity of the detectors to gain in sensitivity

• Size

• Geographical location

• Atmospheric muon background

o First combined point-like source search in the Southern Hemisphere performed in 2015

• (Astrophys.J. 823 (2016) no.1, 65)

o ANTARES data from 2007 to 2012 (6 years) o IceCube from 2008 to 2011 (3 years)

• IC40, IC59, IC79

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ANTARES-IceCube combined analysis

Motivation

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ANTARES-IceCube combined analysis

Extending the analysis

o Adding more years:

- IceCube, 7 years - ANTARES, 9 years o Adding more samples:

- ANTARES

• Tracks

• Cascades - IceCube

• IC40

• IC59

• IC79

• IC86 (4 years)

• Starting tracks (IC79 + IC86 4 years)

Throughgoing tracks

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ANTARES-IceCube combined analysis

Samples

[TeV]

Eν 1

10− 1 10 10² 10³ 10⁴

]2 [meffA

−3

10

2

10−

−1

10 1 10 102

103

Graph

µ CC + ν νµ

ANTARES

e CC + ν νe

ANTARES

µ CC + ν νµ

IC Through-going µ

µ CC + ν νµ

µ IC Starting

Graph

ANTARES -90° < δ < -45°

IC Through-going µ -90° < δ < -30°

IC Starting µ -90° < δ < -5°

[TeV]

Eν

1 10 10² 10³ 10⁴

]° [Ψ∆

−1

10 1

Graph

ANTARES tracks ANTARES cascades IC Through-going µ IC Starting µ

Graph

Effective area Median angular resolution

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ANTARES time correlation analysis

IceCube neutrino candidates

HESE ID Obs. Time (MJD) Decl. (deg.) R.A. (deg.) Med. Angular error (deg.)

3 55451.07075 -31.2 127.9 1.4

5 55512.55163 -0.4 110.6 1.2

8 55608.82013 -21.2 -177.6 1.3

13 55756.11298 40.3 67.9 1.2

18 55923.53182 -24.8 -14.4 1.3

23 55949.56932 -13.2 -151.3 1.9

28 56048.57042 -71.5 164.8 1.3

37 56390.18876 20.7 167.3 1.2

38 56470.11038 14.0 93.3 1.2

43 56628.56885 -22.0 -153.4 1.3

44 56671.87788 0.0 -23.3 1.2

45 56679.20447 -86.3 -141.0 1.2

53 56767.06630 -37.7 -121.0 1.2

§ 13 HESE tracks in the ANTARES field of view (arXiv:1405.5303 , PoS(ICRC2015)1081)

§ Each HESE is treated as potential transient neutrino source

§ Search for astrophysical neutrinos in small time windows around source flares

§ First event observed in September, 2010

§ Last event observed in April, 2014

ANTARES time correlation analysis:

Search method: likelihood

𝑆 9 = 𝑆 :;<=. ⋅ 𝑆 .?.@AB ⋅ 𝑆 Q9O.

𝐵 9 = 𝐵 :;<=. ⋅ 𝐵 .?.@AB ⋅ 𝐵 Q9O.

Signal PDFs

Background PDFs

log𝐿 :'H = I I log 𝜇 :9A J 𝑆 9 J + 𝑁 J 𝐵 9 J − 𝜇 :9A

9∈J J

𝑄 = log𝐿

− log𝐿

Test Statistic

day t₀ day

σ0

σ0 = flare duration t₀ = source obs time

# of data

events per day

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ANTARES time correlation analysis:

5σ Discovery potential for HESE3

(days) σt

1 10 10²

)σ> (50%@5 s <n

0 2 4 6 8 10 12 14 16

18 Time dependent analysis

Time integrated analysis

Time dependent analysis without energy estimator Time integrated analysis without energy estimator

PRELIMINARY

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Expectations for KM3NeT/ARCA

Strategies

q Only up-going track-like events

(estimated contribution from cascades from previous analyses ~ 20%) q Discovery fluxes for:

o Generic point-like source with spectrum ∝E^-2

o Benchmark fluxes from candidate Galactic neutrino sources

v Expected neutrino fluxes estimated from the observed ɣ-ray spectra following [1] (RXJ1713.7-3946(1) from [2]) v Assumptions:

• Hadronic scenario for the ɣ-ray production

• Transparent sources

[1] F. Vissani, Astr. Phys. 26 (2006) 310

[2] S. R. Kelner, Phys. Rev. D 74 (2006), 063007

Φ0 [10^-11TeV^-1 s^-1 cm^-2]

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KM3NeT/ARCA Results:

Galactic Sources analysis

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KM3NeT/ARCA Results:

E

spectrum

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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

Ø No significant clustering at any point of the sky, including the intriguing accumulation close to the galactic center Ø ANTARES is an ideal candidate for a follow-up study of the IceCube “hotspot”

Ø No significant evidence of cosmic neutrino sources found in the last point-source analysis

Ø Most sensitive limits for a large fraction of the Southern Sky set, especially at neutrino energies below 100 TeV Ø NEXT: Expected improvement in the Southern sky combining ANTARES and IceCube data

Ø NEXT: Possibility of constraining the origin of the IceCube astrophysical signal from transient sources Ø Detector combining a km³-size with high visibility towards the Galactic Centre needed

Ø KM3NeT/ARCA is expected to make definite statements about neutrino fluxes from Galactic candidates in a few years of operation

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Backup

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Candidate list

arXiv:1706.01857

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IceCube HESE candidates

arXiv:1706.01857

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Selection criteria

arXiv:1706.01857

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Selection criteria

Track-like events selection cuts

§ Quality parameter: Λ

> -5.2

§ Estimated angular error: β

< 1°

§ Up-going: cosθ

> -0.1

§ Energy estimator: log

(𝜌) > 1.6

§ Muon track length: L

> 360 m

Shower-like events selection cuts

§ Track veto: not selected as track

§ Estimated angular error: β

< 1°

§ Up-going: cosθ

> -0.1

§ Interaction vertex: R

< 300 m, |Z

| < 250 m

§ M-estimator: Mest < 1000

§ Random Decision Forest: RDF > 0.3

§ Muon likelihood: 𝓛

> 50

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Systematic uncertainties

tr) sin(δ

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

Selected track events

0 100 200 300 400 500 600 700 800

PRELIMINARY

sh) sin(δ

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

Selected shower events

0 5 10 15 20 25 30 35

PRELIMINARY

o Absolute Pointing Accuracy Uncertainty

0.13° uncertainty on the horizontal (ϕ) direction 0.06° uncertainty on the vertical (𝜃) direction

o Angular Resolution Uncertainty

15% (12%) degradation on the angular resolution in the track (shower) channel

o Acceptance Uncertainty

15% uncertainty

o Background Uncertainty

declination-dependent distribution of background events parameterized as a linear combination of the two different spline functions (the red and blue

lines)

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The IceCube detector

Antarctic ice

1450 m depth

5160 DOMs

1 km

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The IceCube signal

Six years HESE analysis, events with interaction vertices contained within the instrumented volume PoS(ICRC2017)981

X tracks, + showers Ɣ = 2.92

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The IceCube signal

Six years HESE analysis, events with interaction vertices contained within the instrumented volume PoS(ICRC2017)981

Ɣ = 2.92

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The IceCube signal

Eight years

complementary measurement using CC νµ events where the interaction vertex can be outside this volume PoS(ICRC2017)1005

Purely

atmospheric origin excluded at 5.6σ

significance Ɣ = 2.19

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Neutrino interactions

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