Multi-messenger
astronomy with Icecube
Aya Ishihara (Chiba U)
マルチメッセンジャー天文学研究会(2017/3/2-3@千葉大)
Multimessenger workshop at Chiba U1

Contents• Introduction• Diffuse neutrino flux
• Point source analysis• blazar stacking search• Coincident neutrino with GRB• Other indication?

• Follow-up program and realtime alerts from IceCube• HESE/EHE public alert channel• multiplets alert• gamma-ray follow up• optical/x-ray follow up• Summery
Multimessenger workshop at Chiba U2

The IceCube Detector

1000m

An array of 5160 10’ photomultiplier tubesCherenkov light

digital optical module

1450m

ChargedParticles
2450m

Digitized
Waveform

νl

W,
Zmte
hadronicnl,
νlshower3

BackgroundAtmospheric Neutrinos
cosmic-ray up to knee : n from p and K decay
around and above knee: n from charmed meson decay

Atmospheric neutrino
Decay
νμμ+νμν𝑒𝑒+𝜋+𝜋0

Air Nuclei

γ𝑒−𝝁, 𝝁-bundle
Atmospheric muons
dominant but removable since track-like trajectories of Cherenkov
photons and its directions is able to be reliably reconstructed
Multimessenger workshop at Chiba U4High energy neutrino
detection channels
nm CC only

νlW,Zl,νlmte

hadronicshower〜100TeV up-going muon track event

All except nm CC

Starting event inside detector
sensitive to all flavor CC/NC

Cascade-like events

Cascade +Edep~130TeV
Edep~1.1PeV
PRL 111 (2013) 021103

Phys. Rev. D 84, 072001 (2011)

Science 22 Vol. 342 (2013)
PRL 113, 101101 (2014)5

Diffuse neutrino spectra
Diffuse neutrino flux: Powerful tool to search abandant sources••Accumulate neutrinos from many sources even at very far Universe, or very
weak. Different direction or timing, and of different types
Diffuse flux give hints to build a better point source observation strategy
𝜈 (𝐸 , 𝑧)𝑐𝑑𝑡𝜙𝜈𝜈𝜙𝑑𝑖𝑓𝑓(𝐸𝜈 ) =ඵ𝑑𝑧𝑑Ω
4𝜋𝑑𝑧 𝑑𝐸𝜈 𝑑𝑧

different directionsν

different cosmological distances

ν

ν

ν
ν
ν

ν
ν

ν

ν

ν

ν

ν

ν

unresolved week sources

far sources

SFR: important
contributions upto z~1-26

Upward-going muon track diffuse flux
IceCube ApJ 833 3 (2016)
Energy range of the astrophysical flux: 160TeV - 5.2PeV• 6 year sample
7 year sample– ApJ 833 3(2016)– γ=2.13±0.13• 7 year sample– γ= 2.16±0.11
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Starting event
diffuse flux

3 year (2010/5-2013/5) sample, PRL 113, 101101• Best fit spectral index

was
γ= 2.2 ± 0.4 (2 yrs)
γ= 2.3±0.3 (3 yrs)
and currently
γ= 2.58±0.25 (4 yrs)

4 year sample, ICRC2015 POS (1081)– Energy threshold ~60GeV

Multimessenger workshop at Chiba U8

Reduced threshold starting events
IceCube Phys. Rev. D 91, 022001 (2015)

Lower energy extension of (2 years)
analysis down to 1TeV
γ= 2.46±0.12

Multimessenger workshop at Chiba U

9A best fit comparison• Results are consistentbut,• Keep eye on theinsignificant 2s level oftension between
cascade(≈ reducedstarting) and upward
track analysis

Multimessenger workshop at Chiba U

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11Point source analysis
No clustering observed in starting events(4 yrs)The most significant cluster p-value 58% with all events, 44% with shower events

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Neither in upward-muon sample
6 year sample

13Ingredient for point source analysis
To improve point source sensitivity• Livetime, detector size (cross section of detector in the direction to the object)– sqrt(N)• Angular resolution– linear• Background veto
– Down BG: atm muons, UP BG: atm nu– Surface veto can reduce down muon BG from Southern sky• Neutrino follow up for transient sources - Timing coincident BG cut– GRB• Stacking of the “right” class of object– Hints from diffuse neutrinos, point source upperlimits and gamma-ray observations• Multimessenger!!
– Trigger optical/x-ray/gamma-ray telescopes by neutrino for transient sources

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Tracks: induced by nm CC interaction•

angular resolution
Median resolution: 0.5°at 100 TeV• Moon shadow of cosmic ray muons using one year of data(cosmic-ray primaries get absorbed in moon)

median0.45° ± 0.05°• Background dependent on the directions in the sky
Southern sky: High energy atm muon BG (Signal PeV-EeV)
Northern sky: Atm neutrino BG (signal TeV-PeV)• Large energy resolution for through going-muon asmuon loose energy before reaching IceCube• Δlog(E)~0.3 for muon energy deposit to muonenergy

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Cascade: particle showers
νlW,Z•
••
•

mtel,
νl
hadronicshower

topological selection of cascade events
Good energy resolution of ~10%
Directional resolution is ~10°
Sensitive to full sky
Less atmospheric neutrino background• atm muons are reduced by their topology• turn over energy from BG to signal is lower; sensitive tolower energy region (10TeV – 100TeV)(upward muon channel sensitive above ~100TeV)

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min to year time variability

Source candidates

Need•target photon (or matter)•proton beam (in jet e.g. by shock acceleration)

AGN-blazar
BL Lac PKS 2155−304

GRB and AGNs•
Candidate sources exhibits rapid time variation!

Γ~10

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

optical

x-ray

g-ray bandGRB-correlated neutrino Search
1172 gamma-ray bursts (IceCube 2017, arXive:1702.06868) + 506 GRBs
previously analyzed from GCN and the Fermi GBM database
IceCube2017

Searched temporally and directionally• coincident tracks with– Southern Hemisphere GRB in May 2010 and May
2015 (5 yrs sample)– Northern Hemisphere GRB in May 2008 and May
2015 (7 yrs sample)• coincident cascade with
– All sky GRBs between May 2010 and May 2013 (3yrs sample)

Multimessenger workshop at Chiba U18

Model Dependent Constraints

Combining all channels, 6.5, 11.0 and 0.3 events

Zhang+13
No significant correlation yield tighter constraints on model predictions•internal shock model - radius RIS where protons are accelerated and the radius Rg
where gamma ray photons are generated are the same•
photosphere model - RIS > Rg•
ICMART model (internal collision-induced magnetic reconnection and turbulence) RIS< Rg

Only single zone models – multiple emission region model predict flux lower
thanBench
mark model
IceCube sensitivity

4.7events
2.8events
0.1 events

IceCube2017
Multimessenger workshop at Chiba U19

Model Independent Constraints
Generic broken power-law spectra•More than a factor of 4 improved limits since 2013 nature•

Constrained model predictions normalized to the observed
ultra-high energy cosmic ray flux (10^44 𝑒𝑟𝑔ൗ𝑀𝑝𝑐3 𝑦𝑟)

IceCube2017

GRBs contribute no more than 0.4% of the observed diffuse flux
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blazar stacking analysis
ApJ vol. 835, no. 1, p. 45 (2017)

Neutrinos from Fermi 2LAC 862 blazar directions

Northern sky:
TeV < En < PeV
Southern sky:
simple modeling
En>PeV

Multimessenger workshop at Chiba U21

2LAC blazar 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
Multimessenger workshop at Chiba UHSP

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

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Neutrino weighting
Require: the total # of observed to be the sum of the signal and background events

signal hypothesis PDF
the normalization ns of
the signal contribution

the spectral index ΓSI of thesignal's energy distribution

hypothesis test results

BG is from data

𝑤𝑗 = 𝐶 𝑤𝑗,𝑚𝑜𝑑𝑒𝑙 ∙ 𝑤𝑗,𝑎𝑐𝑐𝑒𝑝𝑡𝑎𝑛𝑐𝑒neutrino luminosity is proportional to gamma-rayluminosity

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Results: Limits on the blazar contribution
UL on E-2.2～2.5 flux

UL on E-2 flux

Equal weighting follows Fermi SCD ApJ, 720:435 (2010)

Contribution of the total 2LAC blazar sample tothe astrophysical neutrino flux
• The equal-weighting upper limit maximally19%27%,• gamma-weighting 7%
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blazar-n correlation search
MNRAS 457 (2016) Padovani

Neutrino sample

Gamma-ray sample

4yr IceCube starting (HESE) events(with conditions >60TeV, <20deg⇒30evts) and 2 yr HE nm sample of
21 through-going m events

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

Multimessenger workshop at Chiba U25

Neutrino events with g-ray counterparts

Nn: the number of n events with at least one g-ray counterpart found within themedian angular error as function of g-ray flux threshold fg• For a Nn (with given catalog, fg), chance probability of randomly producing equalor larger Nn is calculated by randomization of gamma-ray source coordinates –generate ～105 randomized maps
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

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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) inthe first two PeV events• a high fluence blazar PKS B1424-418 outburst showed temporal/positional
coincidence with the third PeV event with an approximate chance coincidence of～5%

7.9evts=

ANTARES did not find events from PKS B1424-418
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IceCube’s followup program overview
Depending on the source classes, most accessible wavelength differs
IceCube public event alert• HESE/EHE Public Events• General purpose high signal/noisesample• GCN alerts to the follow-up
observatories via AMON

Target of Opportunity Program(private alert)• Multiplet• GFU - gamma by imaging atmosphericCherenkov telescopes, longer time scale
upto 3weeks• OFU - optical and x-ray searching timescale upto 100s

gcn.gsfc.nasa.gove/amon.html

Multimessenger workshop at Chiba U28

Extremly High Energy (EHE)
through going muon track• Targets > PeV• Simple detected photo-electron number threshold taking theadvantage of effectively no background in the highest energy
region - as the first hints for the cosmic neutrinos• Modified for alert to select PeV track events• 2.5-4.1 signal events/yr from E-2.49 and E-2 flux with 1.9 BG
events/yr

Multimessenger workshop at Chiba U29

High energy starting muon event• HESE channel dominatescascade events – only sendalert with a higher trackness>6000 photoelectrons
signal neutrinos

Rejectedbackground
eventsabout 1.1 signal-like track-likeevents from an E-2.58 astrophysicalspectrum and about 3.7 total
background events per year30

2016 Public Alerts

AMON ICECUBE_EHE EVENTS – Since June 2016 archived at https://gcn.gsfc.nasa.gov/amon_ehe_events.html

same eventEVENT

OBSERVATION

EventNum_RunNu
mDate

Time UT

NoticeTypeRA

Dec

Error

Signalness

80127519_128906

16/12/10

20:06:40.31

EHE

46.5799+14.9800

60.00

0.4902326552458_128311

16/08/06

12:21:33.00

EHE

122.7980-0.73316.67

0.28016

6888376_128290

16/07/31

01:55:04.00

EHE

214.5440-0.334720.99

0.84879

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

OBSERVATION

EventNum_RunNu
Datem

Time UT

NoticeTypeRA

Dec

Error

ChargeSignalTr

38561326_128672

16/11/03

09:07:31.12

HESE

40.8252+12.5592

66.00

7546.050.30

58537957_128340

16/08/14

21:45:54.00

HESE

199.3100-32.0165

89.39

10431.02

0.126888376_128290

16/07/31

01:55:04.00

HESE

215.1090-0.458173.79

15814.74

0.9167093193_127853

16/04/27

05:52:32.00

HESE

240.5683+9.3417

35.99

18883.62

0.92

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The first GCN notice: HESE-160427A• Event occurred at Wed 27th April 2016 at 05:52:32.00• First notice sent on Wed 27th April 2016 at 05:53:53• Revised coordinates sent at Wed 27th April 2016 at 23:24:24• Event direction RA 16.04deg, Dec 9.34 deg, 90%CL 0.6deg• Follow-up responses➢ GCN 19364 - Fermi Gamma-Ray Burst Monitor - No detection➢ GCN 19360 - Fermi LAT – 5 unrelated blazars➢ GCN 19361 - HAWK – no detection➢ GCN 19362 - MASTER – no detection➢ GCN 19377 - VERITAS – no detection➢ GCN 19392 - iPalomar Transient Factory – 3 transients, all AGN➢ GCN 19427 - FACT Cherenkov TeV Telescope – no detection➢ GCN 19426 - Interplanetary Network – no detection➢ GCN 19381 – Pan-STARRS 6 SN candidates. The most interesting object is PS16cgx which is32
consistent with type Ic supernova at z 0.1-0.2 exploded on/around April 27.2

The multiplet event alert
Event sample: High quality muon track events
Rejecting BG events based on a multivariate classifier• mis-reconstructed events• down-going atmospheric muons for Northern sky (a bittighter cut for GFU than OFU)
• low energy atmospheric muons for Southern sky (GFU only)
Making multipletsOFU• multiple (≥2) neutrino events within 100s an angulardifference of ≤3.5° 𝜟𝜳𝟐
𝜽𝟐𝑨𝜟𝑻
𝝀 = 𝟐 + 𝟐 𝐥𝐧 𝟐𝝅𝝈𝟐𝒒 − 𝟐 𝐥𝐧 𝟏 − 𝐞𝐱𝐩 − 𝟐+ 𝟐𝐥𝐧𝝈𝒘
𝟏𝟎𝟎𝒔• Quality parameter𝝈𝒒• triplet or more automatically sent
GFU
• Each event detected at time ti, define a time window ∆𝑡𝑖𝑗 =𝑖𝑗
𝑡𝑖 − 𝑡𝑗 𝑡𝑗 < 𝑡𝑖 to get the expected background 𝑁𝐵𝐺 using𝑖𝑗

randomized data and the observed 𝑁𝑆𝐼𝐺 .
𝑖𝑗• Poisson probability of observing 𝑁𝑆𝐼𝐺 or larger multiplet
𝑖𝑗with given expected background 𝑁𝐵𝐺 is a quality parameter
33

Optical (x-ray) Follow-up Program
Have been in operation since 2008
Targets• GRB, core-collapse supernovae (SNe), GRB afterglow or the rising SN lightcurve• Less than 1 minute
Alerts are sent to (with different alert quality threshold, all >90% BG):
• the Robotic Optical Transient Search Experiment (ROSTE, from 2008, now
decommissioned) was ～25 alerts/year• Palomar Transient Factory (since 2010) ～7 alerts/year• Swift-XRT for X-ray follow-up (since 2011) ～3 alerts/year• MASTER (since 2016) ～7 alerts/year
M A S T ER
GLOBAL Rob• ASAS-SN (to come soon)
oticNet• LCOGT (to come soon)
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The OFU most significant
alertsarXive:1506.03115• In March 2012, the most significant alert during the first3yrs OFU program was issued• PTF followed up, a Type IIn supernova PTF12csy wasfound 0.2deg away from the neutrino alert direction.
• The supernova has a redshift of z = 0.0684,
corresponding to a luminosity distance of about 300
Mpc• Pan-STARRS1 survey shows that its explosion time
was at least 158 days (in the host-galaxy rest frame)
before the neutrino alert, implying that a causal
connection is unlikely
arXive:1702.06131• In February 2016, the first and only triplet alert to date
was issued• Expected background cumulative rate of this type ofalert is 0.38 since 2008 to the alert time of 2012
Multimessenger workshop at Chiba U35

Gamma-ray Follow up Program
Searches for an excess of neutrino events on time scale of up to 3weeks around sources from a predefined source catalog• Monitored sources based on the Fermi-LAT 2nd catalog, containing mostly BL-Lacobjects and FSRQs, which have exhibited previous variable behavior• Operating since 2012, private alerts to the MAGIC andVERITAS telescopes. HESS in preparation• MAGIC with 0.1 alerts/source/year (3.2σ) total 3BG/yr• Higher threshold for VARITAS (3.6σ) 1BG/yr• 14 March to 31 December 2015, 14 alerts and 4 were
followed up by MAGIC or VERITAS

assuming E-2 for 10
days at declination
28deg• Follow up is not always possible due to limited IACT (moon light,bad weather)
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The GFU most significant alert
Nov 9, 2012 the most interesting alert, six events during 4.17days
with the position of the source SBS 1150+497• pre-trial –log10(pobs)=4.64• post-trial –log10(pobs) = 2.60
VARITAS followed up • Due to poor weather and bright moonlight, VARITAS
could follow only at the end of Nov 12, 2012 night andcontinued to the following night - the total exposure
time 71.5m• No evidence of gamma ray flux

• Setting an integrated flux limit (99%CL) above 300GeVat 3.0 × 10−10 cm−2s−1 for an assumed differential
spectrum with spectral index γ = 2.5.
Multimessenger workshop at Chiba U37

Summary of alert channels
Alert

Event typeCoveragethres E[TeV]MedianAng Res[deg]

Timewindow

Alert rate Alert type
Sig+BG/yr

EHE

through going nmtrack

All sky

～100

0.25

n/a～ 2+2

PublicHESEstarting nm track indetector volume

All sky～60～1.6n/a～ 1+3

PublicGFU

nm track
multiplets

All sky～0.1<1variable,max 21d～2BGs

PrivateNorthern ～0.1sky<1100sVariesPrivateO(X)FU up nm trackmultiplets

Multimessenger workshop at Chiba U38

Summary• IceCube discovered diffuse neutrino flux of which energy budget
consistent with that of UHECR and diffuse gamma-ray background• However, still no significant neutrino event cluster• Limits on the GRB/Blazar components in the observed neutrino flux
• But, there are correlation of HESE/PeV with blazars reported.
• Neutrino triggering follow-up!

• IceCube has started public alert of neutrino events since 2016
• Private alerts in operation since 2008 – and glowing• a couple of interesting SNs (type Ic, type IIn) discovered• Stay tuned for IceCube Gen-2 – Significant point source sensitivity
improvements expected!!
Multimessenger workshop at Chiba U39