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Searching for VHE gamma-ray emission associated with IceCube - - PowerPoint PPT Presentation

Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos using FACT, H.E.S.S., MAGIC and VERITAS Marcos Santander*, Daniela Dorner, Jon Dumm, Konstancja Satalecka, Fabian Schssler for the VERITAS, FACT, IceCube,


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SLIDE 1

Marcos Santander*, Daniela Dorner, Jon Dumm, Konstancja Satalecka, Fabian Schüssler for the VERITAS, FACT, IceCube, MAGIC, and H.E.S.S. Collaborations

*Barnard College - Columbia University

Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos using FACT, H.E.S.S., MAGIC and VERITAS

35th International Cosmic Ray Conference Busan, South Korea — July 12-20, 2017

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SLIDE 2
  • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea

Multi-messenger search for cosmic-ray sources

2

(oscillates to ~1:1:1)

p + p/γ → X + π0 → → X + π+ → µ+ + µ+ → e+ + γγ νµ νe + ¯ νµ

Galactic B-field

γ

ν

p+

Astrophysical beam dump

Spatial/Temporal correlations between neutrinos and gamma rays can trace cosmic-ray acceleration/interaction sites

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SLIDE 3
  • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea

IceCube Collab arxiv/1507.03991

IceCube astrophysical neutrinos

3

IceCube combined spectrum

  • Astrophysical neutrino flux detected in the 20 TeV - 8 PeV energy range
  • Flux consistent with a power-law spectrum with spectral index in the 2.1 - 2.7 range.
  • Data compatible with flavor equipartition.
  • Event rate is low. ~O(10) events / year.

∝ E−2.50±0.09

Conventional atmospheric (νμ + νe)

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SLIDE 4
  • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea

IceCube astrophysical neutrinos

4

arxiv/1510.05223

4-year HE Starting Event (HESE) sky map

  • No point-source detection. Distribution consistent with isotropy.
  • Point-source upper limits at the level of 1%-10% of the all-sky flux hint at large number
  • f sources (N > 10-100).

Search for VHE gamma-ray emission at the positions of likely-astrophysical neutrinos

For 6-year update see NU060 Sat 15th (Claudio Kopper)

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SLIDE 5
  • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea

Imaging Atmospheric Cherenkov Telescopes

5

Khomas Highland (Namibia)

H.E.S.S. MAGIC VERITAS

Canary Islands (Spain) Southern Arizona (USA)

  • Sensitive to VHE (E > 100 GeV) gamma-rays. Effective areas of ~O(105) m2. ~0.1° angular

resolution.

  • Used to observe the location of IceCube neutrino events to search for gamma-ray emission.
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SLIDE 6
  • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea

15°

“Cascade” events

Gamma-ray FoVs and IceCube events

6

HESS-II

VERITAS MAGIC

HESS-I 5° 3.5° 3.2°

“Track” events

~1°

Moon

FACT 4.5°

CC νeντ interactions, NC any flavor CC νµ interactions

Only muon “track” events can be used in the follow-up observations given the IACTs’ field-of-view

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SLIDE 7
  • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea

Selection of IceCube track events for IACT follow-up

7

Visible to FACT/MAGIC/VERITAS Visible to H.E.S.S.

GC

Galactic Plane

Equatorial Coords

  • High-energy muon neutrino events selected from three IceCube event samples:
  • HE starting events (HESE, 13 tracks, arxiv/1510.05223).
  • HE through-going muon tracks, two years (HEMU2, 21 highest-energy events, arxiv/1507.04005).
  • HE through-going muon tracks, six years (HEMU6, 29 highest-energy events, arxiv/1607.08006).
  • Astrophysical probability for the events > 50%.
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SLIDE 8
  • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea

Summary of observations

8

ID RA Dec

  • Ang. res.

H.E.S.S. obs. MAGIC obs. VERITAS obs. [] [] [] time [min] time [min] time [min] HESE-05 110.6

  • 0.4

< 1.2 72

  • 205

HESE-13 67.9 40.3 < 1.2

  • 242

HESE-18 345.6

  • 24.8

< 1.3 486

  • HESE-37

167.3 20.7 < 1.2

  • 447

138 HESE-38 93.3 14.0 < 1.2

  • 342

90 HESE-44 336.7 0.0 < 1.2 432

  • HESE-45

219.0

  • 86.3

< 1.2 270

  • HEMU2-02

88.5 0.2 ∼ 1

  • 133

HEMU2-03 37.1 18.6 ∼ 1

  • 180

HEMU2-05 331.0 11.0 ∼ 1

  • 60

HEMU2-06 346.8 24.0 ∼ 1

  • 115

HEMU2-07 267.5 13.8 ∼ 1

  • 25

HEMU2-08 238.3 18.9 ∼ 1

  • 30

HEMU2-09 235.2 19.3 ∼ 1

  • 30

HEMU2-11 323.3 2.8 ∼ 1

  • 40

HEMU2-13 9.4 7.8 ∼ 1

  • 115

HEMU2-14 207.2 6.7 ∼ 1

  • 76

HEMU2-19 221.9 3.2 ∼ 1

  • 20

HEMU2-20 138.9 47.6 ∼ 1

  • 60

HEMU2-21 31.2 11.8 ∼ 1

  • 60

HEMU6-20 169.61 28.04 < 0.5

  • 50

HEMU6-27 110.63 11.42 < 0.3

  • 648

110 HEMU6-28 100.48 4.56 < 0.3

  • 80

Total exposure [hours] 21.0 24.0 31.0

  • A global exposure of 76 hours has been collected by the three major IACTs.
  • Data sets are analyzed independently by each IACT group.

No VHE gamma-ray excess found in the region of interest of the neutrino events

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SLIDE 9
  • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea

Gamma-ray flux upper limits

9

  • Differential upper limits (95% CL) are calculated at the central neutrino position for all
  • bservations. Median ULs are calculated in 10 energy bins.
  • For reference, the ULs are compared to the IceCube all-sky flux scaled by 10-3.
  • Only valid at the central neutrino position.

0.1% of all-sky IceCube flux

3-year HESE arxiv/1405.5303

IceCube 7-year PS discovery potential arXiv/1609.04981

68% range Full range

ULs from H.E.S.S. and VERITAS

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SLIDE 10
  • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea

Integral gamma-ray upper limit maps

10

  • The neutrino angular uncertainty is

much larger than the IACT PSF.

  • The IACT observations give us good

coverage of the 50% containment region of the neutrino events.

  • We calculate integral upper limits

(95% CL) above an energy threshold for a E-2 spectrum on a regular grid.

  • These ULs give constraints on any

gamma-ray excess or on potential nearby electromagnetic counterparts.

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SLIDE 11
  • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea

Integral gamma-ray upper limit maps

10

50% neutrino containment

  • The neutrino angular uncertainty is

much larger than the IACT PSF.

  • The IACT observations give us good

coverage of the 50% containment region of the neutrino events.

  • We calculate integral upper limits

(95% CL) above an energy threshold for a E-2 spectrum on a regular grid.

  • These ULs give constraints on any

gamma-ray excess or on potential nearby electromagnetic counterparts.

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SLIDE 12
  • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea

IACT pointings

Integral gamma-ray upper limit maps

10

50% neutrino containment

  • The neutrino angular uncertainty is

much larger than the IACT PSF.

  • The IACT observations give us good

coverage of the 50% containment region of the neutrino events.

  • We calculate integral upper limits

(95% CL) above an energy threshold for a E-2 spectrum on a regular grid.

  • These ULs give constraints on any

gamma-ray excess or on potential nearby electromagnetic counterparts.

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SLIDE 13
  • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea

IACT pointings

Integral gamma-ray upper limit maps

10

50% neutrino containment

  • The neutrino angular uncertainty is

much larger than the IACT PSF.

  • The IACT observations give us good

coverage of the 50% containment region of the neutrino events.

  • We calculate integral upper limits

(95% CL) above an energy threshold for a E-2 spectrum on a regular grid.

  • These ULs give constraints on any

gamma-ray excess or on potential nearby electromagnetic counterparts.

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SLIDE 14
  • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea

IACT pointings

Integral gamma-ray upper limit maps

10

50% neutrino containment

  • The neutrino angular uncertainty is

much larger than the IACT PSF.

  • The IACT observations give us good

coverage of the 50% containment region of the neutrino events.

  • We calculate integral upper limits

(95% CL) above an energy threshold for a E-2 spectrum on a regular grid.

  • These ULs give constraints on any

gamma-ray excess or on potential nearby electromagnetic counterparts.

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SLIDE 15
  • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea

IACT pointings

Integral gamma-ray upper limit maps

10

50% neutrino containment

  • The neutrino angular uncertainty is

much larger than the IACT PSF.

  • The IACT observations give us good

coverage of the 50% containment region of the neutrino events.

  • We calculate integral upper limits

(95% CL) above an energy threshold for a E-2 spectrum on a regular grid.

  • These ULs give constraints on any

gamma-ray excess or on potential nearby electromagnetic counterparts.

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SLIDE 16
  • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea

IACT pointings

Integral gamma-ray upper limit maps

10

IACT PSF

50% neutrino containment

  • The neutrino angular uncertainty is

much larger than the IACT PSF.

  • The IACT observations give us good

coverage of the 50% containment region of the neutrino events.

  • We calculate integral upper limits

(95% CL) above an energy threshold for a E-2 spectrum on a regular grid.

  • These ULs give constraints on any

gamma-ray excess or on potential nearby electromagnetic counterparts.

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SLIDE 17
  • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea

IACT pointings

Integral gamma-ray upper limit maps

10

IACT PSF

50% neutrino containment

Upper-limit grid

  • The neutrino angular uncertainty is

much larger than the IACT PSF.

  • The IACT observations give us good

coverage of the 50% containment region of the neutrino events.

  • We calculate integral upper limits

(95% CL) above an energy threshold for a E-2 spectrum on a regular grid.

  • These ULs give constraints on any

gamma-ray excess or on potential nearby electromagnetic counterparts.

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SLIDE 18
  • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea

Upper-limit maps

11

HESE-5 0.2 < ETeV < 20 HESE-44 0.16 < ETeV < 8 HESE-37 ETeV > 0.12 HESE-38 ETeV > 0.12 HESE-13 ETeV > 0.16 HESE-37 ETeV > 0.16

H.E.S.S. MAGIC VERITAS

Flux upper limits in the range ~10-12 - 10-10 cm-2 s-1

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SLIDE 19
  • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea

Upper limits on multi-PeV muon neutrino

12

MAGIC VERITAS - ICRC 2017

50% 99%

  • Highest-energy neutrino detected by IceCube

(~ 8.7 PeV primary energy). patm < 0.01%.

  • Location observed by MAGIC and VERITAS
  • Flux upper limits in the region of interest at

the level of < 10-12 - 10-11 cm-2 s-1

HEMU6-27

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SLIDE 20
  • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea

“Realtime” IceCube neutrino alerts

13

IceCube distributes realtime GCN alerts for muon neutrino events through the AMON network (http://amon.gravity.psu.edu/).

  • ~4 HESE events/year (~1 astrophysical)
  • ~4 EHE muon neutrino events (~2 astrophysical). 0.1° - 0.4°.

AMON GCN Circular

First HESE Alert (04/27/2016) Detection: 05:52:32 UT Alert sent: 05:53:53 UT Delay: 81 seconds

IceCube-160427A

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SLIDE 21
  • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea

VERITAS - ICRC2017

Prompt follow-up IACT observations

14

FACT

4.2 hr obs, ~20 hr delay

MAGIC

  • 2 hrs obs
  • 42 hr delay
  • Ethres ~ 120 GeV

VERITAS

  • 3.2 hrs obs
  • 120s delay

GCN Cicular #19427 GCN Circular #19377

H.E.S.S.

  • 1.7 hrs obs
  • ~ 63 hr delay
  • Ethres ~ 350 GeV

Other follow-ups: 160731A (Circ. #19377), 161103A, AMON160218 Other follow-ups: 161103A Other follow-ups: 160731A, ATel #9315

  • F. Schüssler

Poster GA071

Other follow-ups: 160731A (ATel #9301)

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SLIDE 22
  • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea

Conclusions

  • The major IACT observatories are conducting a search for VHE gamma-

ray emission associated with IceCube high-energy neutrino events.

  • No significant excess in the gamma-ray sky maps found so far. Upper-

limit maps have been derived.

  • Focus now set on performing follow-ups of realtime alerts to increase

the sensitivity to transient or variable sources.

  • Next step: deriving constraints on neutrino source population based
  • n the lack of VHE gamma-ray emission.

15