IC170922A opens up a new window to cosmos!
Aya Ishihara for the IceCube collaboration
Main players@Chiba: Lu Lu, Masaaki Hayashida, Shigeru Yoshida
The 2nd Multi-messenger workshop, Chiba, Japan
2018/3/26

March 26, 20181

Outline• An introduction• Alert-and-follow-up program• The IceCube-170922A event and TXS 0506+056• An independent point source analysis around TXS• Prospects – Questions?

Neutrino as a cosmic messenger

Weak interaction during “propagation”• Penetration power• Pointing capability3

Unsocial neutrino unites UHE sky𝟏𝟏𝑬𝝂 ≈ 𝟐𝟎 𝑬𝑷 ≈ 𝟐 𝑬𝜸

Simple hadronic “creation”• Ingredients– pp or pg interaction– cosmic-ray and target spectra in source• Directly accompanying partners– gamma-ray from neutral pions (p0)– parent cosmic-rays (p, nuclei)• Indirectly accompanying partners– radiations, radio, optical, x-ray...
– Gravitational waves
Multi-messenger !

4

Photopion source candidates
Need•target photon (or matter)•proton beam (in jet e.g. by shock acceleration)
Target photon and beam: GRB and AGNs
•Candidate sources exhibits rapid time variation!

min to year time variability

AGN-blazar
BL Lac PKS 2155−304

Γ~10GRBE～1052erg
Γ ≥100“Typical” Spectral Energy distribution

optical

x-ray

g-ray band

The IceCube Detector

6Detection Principle
An array of photomultiplier tubes + Dark and transparent material

Cherenkov light

ChargedParticles

νl
W,
Zl,
νlmt
e

hadronicshower

Digitized
Waveformn7

Neutrino online alert
IceCube:on-site event analysis andalert system has been in
operation

Iridium satellites

Before 2016 April, private
alert system existed. BUT
only background dominantnhigh energy n

Flare andexposure in theuniverse

Alert!

After 2016: Activated public
online channel with signal
efficiency of >30-50%

Latency time: a few minutes“The IceCube realtime alertsystem”, IceCube
Astroparticle Physics, 92, 30–41,( 2017)

8High energy neutrino signal channels
Upward going track event sensiitve to CC muon neutrino interaction
Phys. Rev. Lett. 115, 081102 (2015)

nm CC onlyνlW,
Zmtel,
νlhadronic
shower>60TeV〜100TeV neutrinos

electromagnetic
and/or hadronic particle showers (cascade)All except n CCStarting event inside detector sensitive to all flavor CC/NCm

Cascade-like events

Cascade +Edep~1.1PeV
Edep~130TeV

PRL 111 (2013) 021103

Phys.
Rev.
D 84,072001(2011)Phys.
Rev.
D 84,072001(2011)

Science 22 Vol. 342 (2013)
PRL 113, 101101 (2014)

9High energy neutrino signal channels
Upward going track event sensiitve to CC muon neutrino interaction
Phys. Rev. Lett. 115, 081102 (2015)

nm CC only

νlW,
Z

mt
el,
νl
hadronic
shower>PeV-10PeV〜100TeV neutrinos

electromagnetic
and/or hadronic particle showers (cascade)All except n CCm

Cascade-like events

Calorimetrical selection of high brightness events
EHE signals: All flavors
elongated cascades and highly stochastic tracks

Edep~1.1PeV
Edep~130TeV

PRL 111 (2013) 021103

Phys.
Rev.
D 84,072001(2011)Phys.
Rev.
D 84,072001(2011)

2 EeV (MC)

2 EeV (MC)10Tracks for better resolution
EHE

track hypothesis chi2

selection
for publicalert

14 events out of 54 HESE events (4yr) are HESE trackspherical

track-likeselectionfor EHE
selectedanalysis

AtmosphericBG

EHE >10PeV

Good angularresolution

𝑆𝑖𝑔𝑛𝑎𝑙_𝑇𝑟𝑎𝑐𝑘𝑛𝑒𝑠𝑠 =ftrack Ptrack
ftrack Ptrack + fshower Pshower + (fbkg /𝑓𝑠𝑖𝑔 ) Pbkg

HE >100TeV

Cosmic Signal
11

Reduced threshold HE
selection is called EHE-alert• Ps are PDF from likelihood ratios e.g. value
from the shower reconstruction divided bythat of the track reconstruction
11• fs are expected ratio of categories

Rates and resolutions
 HESE alert channel Ethres ~100TeV EHE alert channel

Ethres ~100TeV

12

EHE alert acceptance
Largest effective area @ horizon
Largest direction shifts towards downward going with increasing energy(upward muon selection channel)
1EeV
100PeV
100PeV
1EeV
200TeV-1PeV Muon
Energyupward-going

no sensitivity to downward-goingArchived HESE alert events(6 yrs)upward-going

22/82 tracks
downward-going

The most significant cluster p-value 58% with all events, 44% with shower events14« Public » aleart channels

« Public » aleart history• From April (May) 2016 to the end of 2017: 6 EHE alerts and 8 HESE alerts with 1 overlapping event
AMON ICECUBE_EHE EVENTS – Since June 2016 archived at https://gcn.gsfc.nasa.gov/amon_ehe_events.htmlEventNum_RunNum
Date
Time UTRA
Dec
Error(arcmin)

Signalness

17569642_130214

17/11/06

20:54:30.43

340.2500+7.314014.99

0.7459350579430_130033

17/09/22

18:39:39.21

77.2853+5.751714.99

0.5650780305071_129307

17/03/21

07:32:20.69

98.3268-14.4861

19.48

0.280180127519_128906

16/12/10

20:06:40.31

46.5799+14.9800

60.00

0.4902326552458_128311

16/08/06

12:21:33.00

122.7980-0.73316.67

0.28016

6888376_128290

16/07/31

01:55:04.00

214.5440-0.334720.99

0.8487965432
1

same event

AMON ICECUBE_HESE EVENTS – Since April 2016 archived at https://gcn.gsfc.nasa.gov/amon_hese_events.html

EventNum_RunNum Date
34032434_130171 17/10/28
56068624_130126 17/10/15
32674593_129474 17/05/06
65274589_129281 17/03/12
38561326_128672 16/11/03
58537957_128340 16/08/14
6888376_128290
16/07/31
67093193_127853 16/04/27

Time UT
08:28:14.81
1:34:30.06
12:36:55.80
13:49:39.83
09:07:31.12
21:45:54.00
01:55:04.00
05:52:32.00

RA275.0760
162.5790221.6750
304.7300
40.8252
199.3100215.1090
240.5683

Dec+34.5011-15.8611-26.0359-26.2380+12.5592-32.0165-0.4581+9.3417

Error
534.0
73.79
73.79
73.79
66.00
89.39
73.79
35.99

Charge6317.8213906.14
8685.078858.647546.05
10431.02
15814.74
18883.62

SignalTr
0.30
0.51
0.35
0.78
0.30
0.12
0.91
0.92

87
6
5
4
32
116

The 5th EHE aleart: EHE-170922A• Event occurred at 22nd Sept 2017 20:54:30 UTC• First notice sent on 22nd Sept 2017 20:55:13 (43s later) ⇒https://gcn.gsfc.nasa.gov/notices_amon/50579430_130033.amon• Revised coordinates sent 4 hours later ⇒ GCN#21916• Follow-up responses➢ GCN 21917 - Integral - No detection➢ GCN 21923/Atel 10773 - ANTARES - No detection➢ GCN 21924 – HAWC - no detection➢ GCN 21930 - SWIFT XRT - 9 x-ray emitters➢ ATel 10787 - H.E.S.S. – no detection➢ ATel 10791 - Fermi - increased gamma-ray activity of TXS 0506+056 (RA 77.36 deg, Dec +5.69 deg)
➢ ATel 10817 – The First-time detection of VHE gamma rays by MAGIC➢ ....and observations and reports by many more telescopes: AGILE, ASAS-SN, Kapteyn, Kanata, Kiso,Liverpool, Subaru, VERITAS, VLA
17

Point source analysis
Likelihood function: assuming N (= 𝑛𝑠 + 𝑛𝑏 ) events observed
𝑛𝑠𝑛𝑏𝑁• 𝐿 = ς𝑖 ( 𝑃𝑆 + 𝑃𝐵 )𝑁𝑁
• 𝑃𝑆 𝑎𝑛𝑑 𝑃𝐵 𝑎𝑟𝑒 𝑠𝑖𝑔𝑛𝑎𝑙 𝑎𝑛𝑑 𝑏𝑎𝑐𝑘𝑔𝑟𝑜𝑢𝑛𝑑 𝑃𝐷𝐹𝑠

• 𝑃𝑆 = 𝑆𝑝𝑎𝑐𝑖𝑎𝑙 𝑥Ԧ × Energy Ereco , sin 𝜃 × 𝑇𝑒𝑚𝑝𝑜𝑟𝑎𝑙 𝑡
2D Gaussian
𝜃-dependent acceptance x power-law signal flux
Flat, square, Gaussian, or the other model• 𝑃𝐵 = 𝑆𝑝𝑎𝑐𝑖𝑎𝑙 sin 𝜃 × Energy Ereco , sin 𝜃soft spectra ∝E-3.7
spacial distribution of background from off-target sample
Test statistics• 𝑇𝑆 = 2 log

ෞ𝑠𝐿 𝑛𝐿 𝑛𝑠 =0

pseudo-search trials: using off-target, time and azimuth
scrambled sample

What’s next?

19

IceCube

IceCube-Gen2 Facility• Surface array muon veto
 CR physics• Radio array cosmogenic neutrino
 neutrino >10 PeV

Main array• ≈100 strings• ≈100 sensors/string• ≈240m distance

Dense array• 26 strings• 125-192 sensors/string• ≈25m distance21

IceCube to Gen2:
Point source sensitivity• ∝sqrt(x): Livetime, Detector size
• ∝x: Angular resolutionmdefault factor• Signal selection efficiency• BG rejection efficiency

mslightly downgoing horizontal direction is important for>100TeV neutrinos

2018/3/26

Aya Ishihara

22

Gen2 Baseline performance with IceCube DOM• Detector effective muon area
• angular resolution－ x 4～5 (horizontal)－ x ～ 0.45 (horizontal)

default factor gives a factor of 5better sensitivity• Further signal/bg improvements with new optical sensors (cascade and muonreconstruction quality and BG reduction, detector/ice systematics) gives us wider window
2018/3/26

Aya Ishihara

23https://www.nsf.gov/news/news_summ.jsp?cntn_id=244676

Summary• The high energy neutrino alerts and follow up system has been in
operation since 2016, April (HESE) and May (EHE)• Follow-up programs are also in good coordination• 5th EHE alert correlated with gamma-ray flare of the Blazer TXS
0506-056 with significance of 3 sigma• An independent neutrino point-source analysis found correlated
neutrino events in time from direction of the blazer with 3.5 sigma
significance• Modeling of neutrino emission from TXS is not simple – Blazer
can not explain the IceCube diffuse flux
• Of course, this is just a beginning. Hope this is a good start of theVHE neutrino astronomy, which leads to more advanced multimessenger view of Universe
25

Blazer coincidence analysis: classification“two-hump” Spectral Energy distribution

LSP
FSRQ-like

BL Lac-like Radio: FR1 vs FR2
 Optical: FSRQs vs BL Lacs
 SED (synchrotoron-peaked)• LSP low-synchrotron peaked >1014Hz – IR-optical• HSP high-synchrotron peaked >1015Hz – x-rays• ISP intermediate – UV
Essentially all FSRQs are LSPs

HSP
g-ray band
x-ray band
optical band
Fossati+98

26

Neutrino weighting
signal hypothesis PDF
the normalization ns of
the signal contribution

the spectral index ΓSI of thesignal's energy distribution

BG is fromdata

𝑤𝑗 = 𝐶 𝑤𝑗,𝑚𝑜𝑑𝑒𝑙 ∙ 𝑤𝑗,𝑎𝑐𝑐𝑒𝑝𝑡𝑎𝑛𝑐𝑒hypothesis test results
neutrino luminosity is proportional to gammaray luminosity

27

Results: Limits on the blazar contributionUL on E-2 flux

UL on E-2.2～2.5 flux
Equal weighting follows Fermi SCD ApJ, 720:435 (2010)

Contribution of the total 2LAC blazar
sample to the astrophysical neutrino flux
• The equal-weighting upper limit
maximally19%-27%,• gamma-weighting 7%
28

Coincidence of a high-fluence blazar
M. Kadler et al Nature Phys (2016)

TANAMI – Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry – is amultiwavelength program that monitors extragalactic jets of the Southern Sky (δ < −30◦ )• Studied blazars in the 3 PeV events – 6 TANAMI monitoring blazars(mostly FSRQ) in the first two PeV events• a high fluence blazar PKS B1424-418 outburst showedtemporal/positional coincidence with the third PeV event with anapproximate chance coincidence of ～5%

7.9evts=ANTARES did not find events from PKS B1424-418
29

blazar-n correlation search
MNRAS 457 (2016) Padovani

Neutrino sample

Gamma-ray

4yr IceCube starting (HESE)

sampleevents (with conditions>60TeV, <20deg ⇒30evts) and2 yr HE nm sample of 21
through-going m events

Independently built Fermi 2FHL,2WHSP and Fermi 3LAC
catalogues

30

Neutrino events with g-ray counterparts
Nn: the number of n events with at least one g-ray counterpart found within
the median angular error as function of g-ray flux threshold fg• For a Nn (with given catalog, fg), chance probability of randomly producing
equal or larger Nn is calculated by randomization of gamma-ray source
coordinates – generate ～105 randomized maps
MNRAS 457 (2016) Padovani
FSRQs no correlation
non HBLs no correlation

all sample p=24%2FHL•

Correlation of Highsynchrotron peaked
BLLacs with p-valueof 0.4-1.3%

all sample p=1.8%

HBL sample p=1.3%

HBL sample p=0.4%

3LAC

31

Questions• We have UL from blazer stacking analysis – limits on diffuse
nu contribution

Prospects

upward going muon events• 2 year sample• γ=2.2±0.2

PRL 115, 081102 (2015)• 6 year sample• γ=2.13±0.13

ApJ 833 3 (2016)• 7 year sample• γ= 2.16±0.11• 8 year sample• γ= 2.19±0.10

ICRC(2017)35