Neutrino emission from the direction of the blazar TXS 0506+056 …sirius.unist.ac.kr/SRC-CHEA/presentations/2018+2nd+jc... · 2018. 9. 21. · the electromagnetic emission can be

Neutrino emission from the direction of the blazar TXS 0506+056 prior to

the IceCube-170922A alert

IceCube Collaboration

Science, 361, 147, 2018

Multimessenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922A

The IceCube Collaboration, Fermi-LAT, MAGIC, AGILE, ASAS-SN, HAWC, H.E.S.S., INTEGRAL, Kanata, Kiso, Kapteyn, Liverpool

Telescope, Subaru, Swift/NuSTAR, VERITAS, and VLA/17B-403 teams

Science, 361, 147, 2018

Personal Background

• BS in Physics• MS in Nuclear Physics Theory

• Thesis: Gamma-ray Bursts • Ph.D in Computational Astrophysics

• Thesis: Multi-Dimensional Special Relativistic Radiation Hydrodynamics Code• Post-Doc

• Hydrodynamics with non-equilibrium ionization• High velocity clouds and diffuse ISM

• Research Interests• Hydrodynamics with chemical reactions: star forming cloud and evolved stars• Hydrodynamics with nuclear reactions: stellar evolution, explosive phenomena near

compact objects (e.g., X-ray bursts)• Gravitational wave, neutrino astrophysics, and nuclear astrophysics

Introduction

• Blazar as an active galactic nuclei (AGN)• In the relativistic jet, protons and/or

nuclei are accelerated -> cosmic rays• Protons (nuclei) + photons ->

neutral and charged pions ->photons and (muons + neutrinos)• Neutrinos + nuclei in ice/water ->

muons. Charged muons move fasterthan speed of light in the medium andradiate visible photons via Cherenkovradiation.

IceCube-170922A

lower limit of 183 TeV, depending onlyweakly onthe assumed astrophysical energy spectrum (25).The vast majority of neutrinos detected by

IceCube arise from cosmic-ray interactions withinEarth’s atmosphere. Although atmospheric neu-trinos are dominant at energies below 100 TeV,their spectrum falls steeply with energy, allowingastrophysical neutrinos to be more easily identi-fied at higher energies. The muon-neutrino as-

trophysical spectrum, together with simulateddata, was used to calculate the probability that aneutrino at the observed track energy and zenithangle in IceCube is of astrophysical origin. Thisprobability, the so-called signalness of the event(14), was reported to be 56.5% (17). AlthoughIceCube can robustly identify astrophysical neu-trinos at PeV energies, for individual neutrinosat several hundred TeV, an atmospheric origin

cannot be excluded. Electromagnetic observationsare valuable to assess the possible association ofa single neutrino to an astrophysical source.Following the alert, IceCube performed a

complete analysis of relevant data prior to31 October 2017. Although no additional excessof neutrinoswas found from the direction of TXS0506+056 near the time of the alert, there areindications at the 3s level of high-energy neutrino

The IceCube Collaboration et al., Science 361, eaat1378 (2018) 13 July 2018 2 of 8

Fig. 1. Event display forneutrino event IceCube-170922A. The time at which aDOM observed a signal isreflected in the color of the hit,with dark blues for earliest hitsand yellow for latest. Timesshown are relative to the firstDOM hit according to the trackreconstruction, and earlier andlater times are shown with thesame colors as the first andlast times, respectively. Thetotal time the event took tocross the detector is ~3000 ns.The size of a colored sphere isproportional to the logarithmof the amount of lightobserved at the DOM, withlarger spheres correspondingto larger signals. The totalcharge recorded is ~5800 photoelectrons. Inset is an overhead perspective view of the event. The best-fitting track direction is shown as an arrow,

consistent with a zenith angle 5:7þ0:50"0:30 degrees below the horizon.

Fig. 2. Fermi-LATand MAGIC observations of IceCube-170922A’slocation. Sky position of IceCube-170922A in J2000 equatorial coordinatesoverlaying the g-ray counts from Fermi-LAT above 1 GeV (A) and the signalsignificance as observed by MAGIC (B) in this region. The tan squareindicates the position reported in the initial alert, and the green squareindicates the final best-fitting position from follow-up reconstructions (18).Gray and red curves show the 50% and 90% neutrino containment regions,respectively, including statistical and systematic errors. Fermi-LATdata areshown as a photon counts map in 9.5 years of data in units of counts per

pixel, using detected photons with energy of 1 to 300 GeV in a 2° by 2°region around TXS0506+056. The map has a pixel size of 0.02° and wassmoothed with a 0.02°-wide Gaussian kernel. MAGIC data are shown assignal significance for g-rays above 90 GeV. Also shown are the locations ofa g-ray source observed by Fermi-LAT as given in the Fermi-LAT ThirdSource Catalog (3FGL) (23) and the Third Catalog of Hard Fermi-LATSources (3FHL) (24) source catalogs, including the identified positionallycoincident 3FGL object TXS 0506+056. For Fermi-LAT catalog objects,marker sizes indicate the 95% CL positional uncertainty of the source.

RESEARCH | RESEARCH ARTICLE

on September 18, 2018

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Multi-messenger observations: location

lower limit of 183 TeV, depending onlyweakly onthe assumed astrophysical energy spectrum (25).The vast majority of neutrinos detected by

IceCube arise from cosmic-ray interactions withinEarth’s atmosphere. Although atmospheric neu-trinos are dominant at energies below 100 TeV,their spectrum falls steeply with energy, allowingastrophysical neutrinos to be more easily identi-fied at higher energies. The muon-neutrino as-

trophysical spectrum, together with simulateddata, was used to calculate the probability that aneutrino at the observed track energy and zenithangle in IceCube is of astrophysical origin. Thisprobability, the so-called signalness of the event(14), was reported to be 56.5% (17). AlthoughIceCube can robustly identify astrophysical neu-trinos at PeV energies, for individual neutrinosat several hundred TeV, an atmospheric origin

cannot be excluded. Electromagnetic observationsare valuable to assess the possible association ofa single neutrino to an astrophysical source.Following the alert, IceCube performed a

complete analysis of relevant data prior to31 October 2017. Although no additional excessof neutrinoswas found from the direction of TXS0506+056 near the time of the alert, there areindications at the 3s level of high-energy neutrino


Fig. 1. Event display forneutrino event IceCube-170922A. The time at which aDOM observed a signal isreflected in the color of the hit,with dark blues for earliest hitsand yellow for latest. Timesshown are relative to the firstDOM hit according to the trackreconstruction, and earlier andlater times are shown with thesame colors as the first andlast times, respectively. Thetotal time the event took tocross the detector is ~3000 ns.The size of a colored sphere isproportional to the logarithmof the amount of lightobserved at the DOM, withlarger spheres correspondingto larger signals. The totalcharge recorded is ~5800 photoelectrons. Inset is an overhead perspective view of the event. The best-fitting track direction is shown as an arrow,

consistent with a zenith angle 5:7þ0:50"0:30 degrees below the horizon.

Fig. 2. Fermi-LATand MAGIC observations of IceCube-170922A’slocation. Sky position of IceCube-170922A in J2000 equatorial coordinatesoverlaying the g-ray counts from Fermi-LAT above 1 GeV (A) and the signalsignificance as observed by MAGIC (B) in this region. The tan squareindicates the position reported in the initial alert, and the green squareindicates the final best-fitting position from follow-up reconstructions (18).Gray and red curves show the 50% and 90% neutrino containment regions,respectively, including statistical and systematic errors. Fermi-LATdata areshown as a photon counts map in 9.5 years of data in units of counts per

pixel, using detected photons with energy of 1 to 300 GeV in a 2° by 2°region around TXS0506+056. The map has a pixel size of 0.02° and wassmoothed with a 0.02°-wide Gaussian kernel. MAGIC data are shown assignal significance for g-rays above 90 GeV. Also shown are the locations ofa g-ray source observed by Fermi-LAT as given in the Fermi-LAT ThirdSource Catalog (3FGL) (23) and the Third Catalog of Hard Fermi-LATSources (3FHL) (24) source catalogs, including the identified positionallycoincident 3FGL object TXS 0506+056. For Fermi-LAT catalog objects,marker sizes indicate the 95% CL positional uncertainty of the source.




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Multi-messenger observations: lightcurve

emission from that direction in data prior to 2017,as discussed in a companion paper (26).

High-energy g-ray observations ofTXS 0506+056

On 28 September 2017, the Fermi Large AreaTelescope (LAT) Collaboration reported that thedirection of origin of IceCube-170922A was con-sistent with a known g-ray source in a state ofenhanced emission (16). Fermi-LAT is a pair-conversion telescope aboard the Fermi Gamma-ray Space Telescope sensitive to g-rays with energiesfrom 20MeV to greater than 300 GeV (27). SinceAugust 2008, it has operated continuously, pri-marily in an all-sky survey mode. Its wide fieldof view of ~2.4 steradian provides coverage of theentire g-ray sky every 3 hours. The search for pos-sible counterparts to IceCube-170922Awas part ofthe Fermi-LAT collaboration’s routinemultiwave-length, multimessenger program.Inside the error region of the neutrino event,

a positional coincidence was found with a pre-viously cataloged g-ray source, 0.1° from the best-fitting neutrino direction. TXS 0506+056 is ablazar of BLLacertae (BLLac) type. Its redshift ofz ¼ 0:3365T0:0010was measured only recentlybased on the optical emission spectrum in astudy triggered by the observation of IceCube-170922A (28).

TXS 0506+056 is a known Fermi-LAT g-raysource, appearing in three catalogs of Fermisources (23, 24, 29) at energies above 0.1, 50, and10 GeV, respectively. An examination of theFermi All-Sky Variability Analysis (FAVA) (30)photometric light curve for this object showedthat TXS 0506+056 had brightened consider-ably in the GeV band starting in April 2017 (16).Independently, a g-ray flare was also found byFermi ’s Automated Science Processing [ASP (25)].Such flaring is not unusual for a BLLac object andwould not have been followed up as extensively ifthe neutrino were not detected.Figure 3 shows the Fermi-LAT light curve and

the detection time of the neutrino alert. The lightcurve of TXS 0506+056 from August 2008 toOctober 2017was calculated in bins of 28 days forthe energy range above 0.1 GeV. An additionallight curve with 7-day bins was calculated for theperiod around the time of the neutrino alert. Theg-ray flux of TXS 0506+056 in each time bin wasdetermined through a simultaneous fit of thissource and the other Fermi-LAT sources in a10° by 10° region of interest along with theGalactic and isotropic diffuse backgrounds, usinga maximum-likelihood technique (25). The inte-grated g-ray flux of TXS 0506+056 forE> 0.1 GeV,averaged over all Fermi-LAT observations span-ning 9.5 years, is ð7:6 T 0:2Þ $ 10% 8 cm% 2 s% 1. The

highest flux observed in a single 7-day light curvebin was ð5:3 T 0:6Þ $ 10% 7 cm% 2 s% 1, measured inthe week 4 to 11 July 2017. Strong flux variationswere observed during the g-ray flare, themost prom-inent being a flux increase from ð7:9 T 2:9Þ$10% 8 cm% 2 s% 1 in the week 8 to 15 August 2017to ð4:0 T 0:5Þ $ 10% 7 cm% 2 s% 1 in the week 15 to22 August 2017.The Astro-Rivelatore Gamma a Immagini Leg-

gero (AGILE) g-ray telescope (31) confirmed theelevated level of g-ray emission at energies above0.1 GeV from TXS 0506+056 in a 13-day window(10 to 23 September 2017). The AGILEmeasuredfluxofð5:3 T 2:1Þ $ 10% 7 cm% 2 s% 1 is consistentwiththe Fermi-LAT observations in this time period.High-energy g-ray observations are shown in

Figs. 3 and4.Details on theFermi-LAT andAGILEanalyses can be found in (25).

Very-high-energy g-ray observations ofTXS 0506+056

Following the announcement of IceCube-170922A,TXS 0506+056 was observed by several ground-based Imaging Atmospheric Cherenkov Tele-scopes (IACTs). A total of 1.3 hours of observationsin the direction of the blazar TXS 0506+056were taken using the High-Energy StereoscopicSystem (H.E.S.S.) (32), located in Namibia, on23 September 2017 [Modified Julian Date (MJD)


A

B

C

D

E

F

-

Fig. 3. Time-dependent multiwavelength observations of TXS0506+056 before and after IceCube-170922A. Significant variability ofthe electromagnetic emission can be observed in all displayed energybands, with the source being in a high-emission state around thetime of the neutrino alert. From top to bottom: (A) VHE g-rayobservations by MAGIC, H.E.S.S., and VERITAS; (B) high-energy g-rayobservations by Fermi-LAT and AGILE; (C and D) x-ray observations bySwift XRT; (E) optical light curves from ASAS-SN, Kiso/KWFC, andKanata/HONIR; and (F) radio observations by OVRO and VLA. The red

dashed line marks the detection time of the neutrino IceCube-170922A.The left set of panels shows measurements between MJD 54700(22 August 2008) and MJD 58002 (6 September 2017). The set ofpanels on the right shows an expanded scale for time rangeMJD 58002 to MJD 58050 (24 October 2017). The Fermi-LAT lightcurve is binned in 28-day bins on the left panel, while finer 7-day binsare used on the expanded panel. A VERITAS limit from MJD 58019.40(23 September 2017) of 2:1 $ 10% 10 cm% 2 s% 1 is off the scale of the plotand not shown.




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Multi-messenger observations: spectrum

58019], ~4 hours after the circulation of the neu-trino alert. A 1-hour follow-up observation of theneutrino alert under partial cloud coverage wasperformed using the Very Energetic RadiationImaging Telescope Array System (VERITAS) g-raytelescope array (33), located in Arizona, USA, lateron the same day, ~12 hours after the IceCubedetection. Both telescopes made additional obser-vations on subsequent nights, but neither detectedg-ray emission from the source [see Fig. 3 and(25)]. Upper limits at 95% CL on the g-ray fluxwere derived accordingly (assuming the mea-sured spectrum, see below): 7:5! 10"12 cm"2 s"1

during the H.E.S.S. observation period and 1:2!10"11 cm"2 s"1 during the VERITAS observations,both for energies E >175 GeV.The Major Atmospheric Gamma Imaging

Cherenkov (MAGIC) Telescopes (34) observedTXS 0506+056 for 2 hours on 24 September 2017(MJD 58020) under nonoptimal weather con-ditions and then for a period of 13 hours from28 September to 4 October 2017 (MJD 58024–58030) under good conditions. MAGIC consistsof two 17-m telescopes, located at the Roque delos Muchachos Observatory on the CanaryIsland of La Palma (Spain).No g-ray emission from TXS 0506+056 was

detected in the initial MAGIC observations on24 September 2017, and an upper limit was derivedon the flux above 90 GeV of 3:6! 10"11 cm"2 s"1

at 95% CL (assuming a spectrumdN=dEºE"3:9).However, prompted by the Fermi-LAT detectionof enhanced g-ray emission, MAGIC performedanother 13 hours of observations of the regionstarting 28 September 2017. Integrating the data,MAGIC detected a significant very-high-energy(VHE) g-ray signal (35) corresponding to 374 ±62 excess photons, with observed energies up toabout 400 GeV. This represents a 6.2s excess overexpected background levels (25). The day-by-daylight curve of TXS 0506+056 for energies above90 GeV is shown in Fig. 3. The probability that aconstant flux is consistent with the data is lessthan 1.35%. The measured differential photonspectrum (Fig. 4) can be described over the energyrange of 80 to 400 GeV by a simple power law,dN=dEºEg, with a spectral index g="3:9 T 0.4and a flux normalization of (2.0 T 0.4) ! 10"10

TeV"1 cm"2 s"1 atE = 130 GeV. Uncertainties arestatistical only. The estimated systematic uncer-tainties are <15% in the energy scale, 11 to 18% inthe flux normalization, and ±0.15 for the power-law slope of the energy spectrum (34). Furtherobservations after 4 October 2017 were preventedby the full Moon.An upper limit to the redshift of TXS 0506+056

can be inferred from VHE g-ray observationsusing limits on the attenuation of the VHE fluxdue to interaction with the EBL. Details on themethod are available in (25). The obtained upper

limit ranges from 0.61 to 0.98 at a 95% CL, de-pending on the EBL model used. These upperlimits are consistent with the measured redshiftof z ¼ 0:3365 (28).No g-ray source above 1 TeV at the location of

TXS 0506+056 was found in survey data of theHigh Altitude Water Cherenkov (HAWC) g-rayobservatory (36), either close to the time of theneutrino alert or in archival data taken sinceNovember 2014 (25).VHE g-ray observations are shown in Figs. 3

and 4. All measurements are consistent with theobserved flux from MAGIC, considering the dif-ferences in exposure, energy range, and obser-vation periods.

Radio, optical, and x-ray observations

The Karl G. Jansky Very Large Array (VLA) (37)observed TXS 0506+056 starting 2 weeks afterthe alert in several radio bands from 2 to 12 GHz(38), detecting significant radio flux variabilityand some spectral variability of this source. Thesource is also in the long-term blazar monitoringprogram of the Owens Valley Radio Observatory(OVRO) 40-m telescope at 15 GHz (39). The lightcurve shows a gradual increase in radio emissionduring the 18months preceding the neutrino alert.Optical observations were performed by

the All-Sky Automated Survey for Supernovae(ASAS-SN) (40), the Liverpool Telescope (41), the


Fig. 4. Broadband spectralenergy distribution for the blazarTXS 0506+056. The SED isbased on observations obtainedwithin 14 days of the detection ofthe IceCube-170922A event. TheE2dN=dE vertical axis is equivalentto a nFn scale. Contributions areprovided by the followinginstruments: VLA (38), OVRO(39), Kanata Hiroshima Opticaland Near-InfraRed camera(HONIR) (52), Kiso, and the KisoWide Field Camera (KWFC) (43),Southeastern Association forResearch in Astronomy Observa-tory (SARA/UA) (53), ASAS-SN(54), Swift Ultraviolet and OpticalTelescope (UVOT) and XRT (55),NuSTAR (56), INTEGRAL (57),AGILE (58), Fermi-LAT (16),MAGIC (35),VERITAS (59), H.E.S.S.(60), and HAWC (61). Specificobservation dates and times areprovided in (25). Differential fluxupper limits (shown as coloredbands and indicated as “UL” in the legend) are quoted at the 95% CL,while markers indicate significant detections. Archival observations areshown in gray to illustrate the historical flux level of the blazar in theradio-to-keV range as retrieved from the ASDC SED Builder (62), and in theg-ray band as listed in the Fermi-LAT 3FGL catalog (23) and from ananalysis of 2.5 years of HAWC data. The g-ray observations have not beencorrected for absorption owing to the EBL. SARA/UA, ASAS-SN, andKiso/KWFC observations have not been corrected for Galactic attenua-tion. The electromagnetic SED displays a double-bump structure, one

peaking in the optical-ultraviolet range and the second one in the GeVrange, which is characteristic of the nonthermal emission from blazars.Even within this 14-day period, there is variability observed in several of theenergy bands shown (see Fig. 3), and the data are not all obtainedsimultaneously. Representative nm þ !nm neutrino flux upper limits thatproduce on average one detection like IceCube-170922A over a periodof 0.5 (solid black line) and 7.5 years (dashed black line) are shown,assuming a spectrum of dN=dEºE"2 at the most probable neutrinoenergy (311 TeV).




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Neutrino emission from the direction of the blazar TXS 0506+056 prior to the IceCube-170922A alert ?

• Search signal by using four parameters • Astrophysical neutrinos have different spectral index than

atmospheric neutrinos

• Time-dependent and time-integrated search

as a fitted parameter. Themodel parameters arecorrelated and are expressed as a pair, (F100, g),where F100 is the flux normalization at 100 TeV.The time-dependent analysis uses the same for-mulation of the likelihood but searches forclustering in time aswell as space by introducingan additional time profile. It is performed sep-arately for two different generic profile shapes: aGaussian-shaped timewindow and a box-shapedtime window. Each analysis varies the centraltime of the window, T0, and the duration TW(from seconds to years) of the potential signal tofind the four parameters (F100, g, T0, TW) thatmaximize the likelihood ratio, which is definedas the test statistic TS. (For the Gaussian timewindow, TW represents twice the standard de-viation.) The test statistic includes a factor thatcorrects for the look-elsewhere effect arisingfrom all of the possible time windows that couldbe chosen (30).For each analysis method (time-integrated and

time-dependent), a robust significance estimate isobtained by performing the identical analysis ontrialswith randomizeddatasets. These areproducedby randomizing the event times and recalculating

theRAcoordinateswithin eachdata-takingperiod.The resultant P value is defined as the fraction ofrandomized trials yieldinga valueofTSgreater thanor equal to the one obtained for the actual data.Because the detector configuration and event

selections changed as shown in Table 1, the time-dependent analysis is performed by operating oneach data-taking period separately. (A flare thatspans a boundary between two periods could bepartially detected in either period, but with re-duced significance.) An additional look-elsewherecorrection then needs to be applied for a result inan individual data segment, given by the ratio ofthe total 9.5-year observation time to the obser-vation time of that data segment (30).

Neutrinos from the direction ofTXS 0506+056

The results of the time-dependent analysis per-formed at the coordinates of TXS 0506+056 areshown in Fig. 1 for each of the six data periods.One of the data periods, IC86b from2012 to 2015,contains a significant excess, which is identifiedby both time-window shapes. The excess consistsof 13 ± 5 events above the expectation from theatmospheric background. The significancedependson the energies of the events, their proximity tothe coordinates of TXS 0506+056, and theirclustering in time. This is illustrated in Fig. 2,which shows the time-independent weight ofindividual events in the likelihood analysis duringthe IC86b data period.The Gaussian time window is centered at 13

December 2014 [modified Julianday (MJD) 57004]with an uncertainty of ±21 days and a durationTW = 110þ35

"24 days. The best-fitting parameters forthe fluence J100 = ∫F100(t)dtand the spectralindex are givenbyE2J100=2:1þ0:9

"0:7 # 10"4 TeVcm–2

at 100 TeV and g = 2.1 ± 0.2, respectively. Thejoint uncertainty on these parameters is shownin Fig. 3 along with a skymap showing the resultof the time-dependent analysis performed at thelocation of TXS 0506+056 and in its vicinityduring the IC86b data period.The box-shaped time window is centered

13 days later with duration TW = 158 days (fromMJD 56937.81 to MJD 57096.21, inclusive of

contributing events at boundary times). For thebox-shaped time window, the uncertainties arediscontinuous and not well defined, but the un-certainties for the Gaussian window show that itis consistent with the box-shaped time windowfit. Despite the different window shapes, whichlead to different weightings of the events as afunction of time, bothwindows identify the sametime interval as significant. For the box-shapedtime window, the best-fitting parameters are sim-ilar to those of the Gaussianwindow, with fluenceat 100 TeV and spectral index given by E2J100 =2:2þ1:0

"0:8 # 10"4 TeV cm–2 and g = 2.2 ± 0.2. Thisfluence corresponds to an average flux over158 days of F100 = 1:6þ0:7

"0:6 # 10"15 TeV–1 cm–2 s–1.Whenwe estimate the significance of the time-

dependent result by performing the analysis atthe coordinates of TXS 0506+056 on randomizeddatasets, we allow in each trial a new fit for allthe parameters: F100, g, T0, TW. We find that thefraction of randomized trials that result in a moresignificant excess than the real data is 7 × 10–5 forthe box-shaped time window and 3 × 10–5 for theGaussian time window. This fraction, once cor-rected for the ratio of the total observation timeto the IC86b observation time (9.5 years/3 years),results in P values of 2 × 10–4 and 10–4, respec-tively, corresponding to 3.5s and 3.7s. Becausethere is no a priori reason to prefer one of thegeneric timewindows over the other, we take themore significant one and include a trial factor of2 for the final significance, which is then 3.5s.Outside the 2012–2015 time period, the next

most significant excess is found using the Gauss-ian window in 2017 and includes the IceCube-170922A event. This time window is centeredat 22 September 2017 with duration TW = 19 days,g = 1.7 ± 0.6, and fluence E2J100 = 0:2þ0:4

"0:2 # 10"4

TeV cm–2 at 100 TeV. No other event besides theIceCube-170922A event contributes significantlyto the best fit. As a consequence, the uncertaintyon the best-fitting window location and widthspans the entire IC86c period, because any win-dow containing IceCube-170922A yields a similarvalue of the test statistic. Following the trial cor-rectionprocedure for different observationperiodsas described above, the significance of this excess

IceCube Collaboration, Science 361, 147–151 (2018) 13 July 2018 2 of 5

Table 1. IceCube neutrino data samples.Six data-taking periods make up the full9.5-year data sample. Sample numberscorrespond to the number of detectorstrings that were operational. During thefirst three periods, the detector was stillunder construction. The last three periodscorrespond to different data-takingconditions and/or event selections with thefull 86-string detector.

Sample Start End

IC40 5 April 2008 20 May 2009.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ..

IC59 20 May 2009 31 May 2010.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ..

IC79 31 May 2010 13 May 2011.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ..

IC86a 13 May 2011 16 May 2012.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ..

IC86b 16 May 2012 18 May 2015.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ..

IC86c 18 May 2015 31 October 2017.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ..

Fig. 1. Time-dependent analysis results. The orange curve correspondsto the analysis using the Gaussian-shaped time profile. The central time T0

and width TW are plotted for the most significant excess found in eachperiod, with the P value of that result indicated by the height of the peak.The blue curve corresponds to the analysis using the box-shaped timeprofile. The curve traces the outer edge of the superposition of the best-

fitting time windows (durations TW) over all times T0, with the heightindicating the significance of that window. In each period, the mostsignificant time window forms a plateau, shaded in blue. The large blueband centered near 2015 represents the best-fitting 158-day time windowfound using the box-shaped time profile. The vertical dotted line in IC86cindicates the time of the IceCube-170922A event.




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Sample Start End

IC40 5 April 2008 20 May 2009.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ..

IC59 20 May 2009 31 May 2010.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ..

IC79 31 May 2010 13 May 2011.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ..

IC86a 13 May 2011 16 May 2012.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ..

IC86b 16 May 2012 18 May 2015.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ..

IC86c 18 May 2015 31 October 2017.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ..







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"0:2 # 10"4




Sample Start End

IC40 5 April 2008 20 May 2009.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ..

IC59 20 May 2009 31 May 2010.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ..

IC79 31 May 2010 13 May 2011.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ..

IC86a 13 May 2011 16 May 2012.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ..

IC86b 16 May 2012 18 May 2015.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ..

IC86c 18 May 2015 31 October 2017.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ..







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Time-dependent search

Estimating parameters

is 1.4s. If the IceCube-170922A event is removed,no excess remains during this time period. Thisagrees with the result of the rapid-response anal-ysis (31) that is part of the IceCube alert program,which found no other potential astrophysicalneutrinos from the same region of the sky during±7 days centered on the time of IceCube-170922A.We performed a time-integrated analysis at

the coordinates of TXS 0506+056 using the full9.5-year data sample. The best-fitting parametersfor the flux normalization and the spectral indexareF100 = 0:8þ0:5

"0:4 # 10"16 TeV–1 cm–2 s–1 and g =2.0 ± 0.3, respectively. The joint uncertainty onthese parameters is shown in Fig. 4A. The P value,based on repeating the analysis at the same co-ordinates with randomized datasets, is 0.002%(4.1s), but this is an a posteriori significanceestimate because it includes the IceCube-170922Aevent, whichmotivated performing the analysis atthe coordinates of TXS 0506+056. An unbiased

significance estimate including the event wouldneed to take into account the look-elsewhere effectrelated to all other possible directions in the skythat could be analyzed. It is expected that therewill be two or three directions somewhere in thenorthern sky with this significance or greater,resulting from the chance alignment of neutri-nos (12). Here, we are interested in determiningwhether there is evidence of time-integrated neu-trino emission from TXS 0506+056 besides theIceCube-170922A event.If we remove the final data period IC86c, which

contains the event, and perform the analysisagain using only the first 7 years of data, we findbest-fitting parameters that are nearly unchanged:F100 =0:9þ0:6

"0:5 # 10"16 TeV–1 cm–2 s–1 and g = 2.1 ±0.3, respectively. The joint uncertainty on theseparameters is shown in Fig. 4B. The P value, usingonly the first 7 years of data, is 1.6% (2.1s), basedon repeating the analysis at the same coordinates

with randomized datasets. These results indicatethat the time-integrated fit is dominated by thesame excess as found in the time-dependentanalysis above, having similar values for thespectral index and total fluence (E2J100 = 2.0 ×10–4 TeV cm–2 at 100 TeV over the 7-year period).This excess is not significant in the time-integratedanalysis because of the additional backgroundduring the rest of the 7-year period.

Blazars as neutrino sources

The signal identified during the 5-month periodin 2014–2015 consists of an estimated 13 ± 5muon-neutrino events that are present in addi-tion to the expected background. The analysis isunbinned, but the mean background at the dec-lination of TXS 0506+056 is useful for compar-ison purposes; it is 5.8 events in a search bin ofradius 1° during a 158-day time window. (We usethe duration of the box-shaped time window re-sult for convenience to calculate averages duringthe flare.) The significance of the excess is due toboth the number of events and their energydistribution, with higher-energy events increasingthe significance and leading to the best-fittingspectral index of 2.1, in contrast to the lower-energy atmospheric neutrino background withspectral index ~3.7. At this declination in the sky,the 68% central energy range inwhich IceCube ismost sensitive to point sources with E–2.1 spectrais between 32 TeV and 3.6 PeV. Assuming thatthe muon-neutrino fluence (E2J100 = 2:1þ1:0

"0:7#10"4 TeV cm–2) is one-third of the total neu-trino fluence, then the all-flavor neutrino energyfluence is 4:2þ2:0

"1:4 # 10"3 erg cm–2 over thisenergy range. With the recent measurement (32)of the redshift of TXS 0506+056 as z = 0.3365 ±0.0010, this energy fluence implies that the iso-tropic neutrino luminosity is 1:2þ0:6

"0:4 # 1047 erg s–1

averaged over 158 days. This is higher than theisotropic gamma-ray luminosity during the sameperiod, which is similar to the long-term luminositybetween 0.1 GeV and 100 GeV of 0.28 × 1047 ergs–1 averaged over all Fermi-LAT observations ofTXS 0506+056 (20). Gamma rays are expected to


Fig. 2. Time-independent weight of individual events during the IC86b period. Each vertical linerepresents an event observed at the time indicated by calendar year (top) or MJD (bottom).Overlapping lines are shifted by 1 to 2 days for visibility. The height of each line indicates the eventweight: the product of the event’s spatial term and energy term in the unbinned likelihood analysisevaluated at the location of TXS 0506+056 and assuming the best-fitting spectral index g = 2.1(30).The color for each event indicates an approximate value in units of TeVof the reconstructed muonenergy (muon energy proxy), which the analysis compares with expected muon energy distributionsunder different hypotheses. [A distribution for the true neutrino energy of a single event can alsobe inferred from the event’s muon energy (30).] The dashed curve and the solid bracket indicate thebest-fitting Gaussian and box-shaped time windows, respectively. The distribution of event weightsand times outside of the best-fitting time windows is compatible with background.

Fig. 3. Time-dependent analy-sis results for the IC86b dataperiod (2012–2015).(A) Change in test statistic,DTS, as a function of the spectralindex parameter g and the fluenceat 100 TeV given by E2J100. Theanalysis is performed at thecoordinates of TXS 0506+056,using the Gaussian-shaped timewindow and holding the timeparameters fixed (T0 = 13December 2014, TW = 110 days).The white dot indicates the best-fitting values. The contours at68% and 95% confidence levelassuming Wilks’ theorem (36) areshown in order to indicate the statistical uncertainty on the parameterestimates. Systematic uncertainties are not included. (B) Skymap showingthe P value of the time-dependent analysis performed at the coordinates ofTXS 0506+056 (cross) and at surrounding locations.The analysis is

performed on the IC86b data period, using the Gaussian-shaped time window.At each point, the full fit for (F, g, T0, TW) is performed.The P value showndoes not include the look-elsewhere effect related to other data periods. Anexcess of events is detected, consistent with the position of TXS 0506+056.




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be produced in the same processes that produceneutrinos—for example, when accelerated pro-tons interact with ambient lower-energy photonsnear the source, producing both neutral pions(which decay to gamma rays) and chargedpions (which decay to neutrinos and leptons). Ahigher luminosity in neutrinos than in gammarays could imply that a substantial fraction ofthe gamma rays related to the neutrino produc-tion are either absorbed or arriving at energiesabove or below the Fermi-LAT energy band.Although TXS 0506+056 is a bright object in

gamma rays, it was not previously singled out asa predicted neutrino source. In the third catalogof active galactic nuclei detected by Fermi-LAT(33) listing 1773 objects (including those at lowgalactic latitudes), TXS 0506+056 is among the50 brightest objects, with an average flux be-tween 1 GeV and 100 GeV of 6.5 (±0.2) × 10–9

photons cm–2 s–1. Its measured redshift nowmakes it one of themost luminous objects knownout to the same distance, more than an order ofmagnitude more luminous than nearby blazarssuch as Markarian 421, Markarian 501, and 1ES1959+650. With respect to these objects, animportant observational distinction is the fa-vorable declination of TXS 0506+056. As theneutrino-nucleon interaction cross section growswith energy, absorption in Earth becomes con-siderable for neutrinos above ~100 TeV. IceCubeis most sensitive to high-energy neutrinosfrom sources at declinations near the equatorialplane, which is viewed along the horizon fromthe South Pole. The blazars mentioned aboveare at more northern declinations, and the like-lihood that a neutrino with energy of ~300 TeVfrom one of these will be absorbed while travers-ing Earth is three to five times the likelihood thatit will reach the detector. The explanation forwhy TXS 0506+056 is the first blazar associatedwith a significant neutrino excess may there-fore depend on the combination of its intrinsicproperties and the observational properties ofthe detector.IceCube recently published (34) a search for

neutrino emission from the blazars in the secondcatalog of active galactic nuclei detected by Fermi-LAT (35), constraining their contribution to thediffuse astrophysical neutrino flux under different

model assumptions. An upper limit of 27% wasfound assuming the diffuse flux that is fit between10 TeV and 100 TeV with a soft E–2.5 spectrum(16). For an E–2 spectrum compatible with thediffuse flux fit above ~200 TeV (17), the upperlimit is between 40% and 80%. The allowed con-tribution by blazars as a population is larger, be-cause it would include the contribution of fainterand more distant blazars not yet resolved in thecatalog. Averaged over 9.5 years, the neutrino fluxof TXS 0506+056 by itself corresponds to 1% ofthe astrophysical diffuse flux and is fully com-patible with the previous blazar catalog results.The evidence presented above supports the

hypothesis presented in (20) that the blazar TXS0506+056 is a high-energy neutrino source. The3.5s evidence for neutrino emission during the5-month period in 2014–2015 is statistically in-dependent of the evidence presented in (20).The analysis of the IceCube-170922A event in(20) relies on correlation of a single neutrino withelectromagnetic activity, whereas the analysispresented here relies only on self-correlationof multiple neutrinos. The coincidence of anIceCube alert with a flaring blazar, combinedwith a neutrino flare from the same object inarchival IceCube data, pinpoints a likely sourceof high-energy cosmic rays.

REFERENCES AND NOTES

1. Pierre Auger Collaboration, Science 357, 1266–1270(2017).

2. F. Reines, Annu. Rev. Nucl. Part. Sci. 10, 1–26 (1960).3. C. M. Urry, P. Padovani, Publ. Astron. Soc. Pac. 107, 803

(1995).4. K. Mannheim, Astropart. Phys. 3, 295–302 (1995).5. F. Halzen, E. Zas, Astrophys. J. 488, 669–674 (1997).6. A. Mücke, R. J. Protheroe, R. Engel, J. P. Rachen, T. Stanev,

Astropart. Phys. 18, 593–613 (2003).7. K. Murase, in Neutrino Astronomy, T. Gaisser, A. Karle, Eds.

(World Scientific, 2017), pp. 15–31.8. M. Petropoulou, C. D. Dermer, Astrophys. J. Lett. 825, L11

(2017).9. C. Guépin, K. Kotera, Astron. Astrophys. 603, A76 (2017).10. M.-H. Ulrich, L. Maraschi, C. M. Urry, Annu. Rev. Astron.

Astrophys. 35, 445–502 (1997).11. M. G. Aartsen et al., J. Instrum. 12, P03012 (2017).12. M. G. Aartsen et al., Astrophys. J. 835, 151 (2017).13. M. G. Aartsen et al., Phys. Rev. D 89, 102004 (2014).14. IceCube Collaboration, Science 342, 1242856 (2013).15. M. G. Aartsen et al., Phys. Rev. Lett. 113, 101101 (2014).16. M. G. Aartsen et al., Astrophys. J. 809, 98 (2015).17. M. G. Aartsen et al., Astrophys. J. 833, 3 (2016).

18. M. G. Aartsen et al., Astrophys. J. 807, 46 (2015).19. E. Massaro et al., Astrophys. Space Sci. 357, 75 (2015).20. IceCube, Fermi-LAT, MAGIC, AGILE, ASAS-SN, HAWC, H.E.S.S.,

INTEGRAL, Kanata, Kiso, Kapteyn, Liverpool Telescope, Subaru,Swift/NuSTAR, VERITAS, and VLA/17B-403 teams, Science361, eaat1378 (2018).

21. M. G. Aartsen et al., Astropart. Phys. 92, 30–41 (2017).22. IceCube Collaboration, GRB Coordinates Network, Circular Service

21916 (2017); https://gcn.gsfc.nasa.gov/gcn3/21916.gcn3.23. Y. T. Tanaka, S. Buson, D. Kocevski, Astronomer’s

Telegram 10791 (2017); www.astronomerstelegram.org/?read=10791.

24. W. B. Atwood et al., Astrophys. J. 697, 1071–1102 (2009).25. J. Aleksić et al., Astropart. Phys. 35, 435–448 (2012).26. R. Mirzoyan, Astronomer’s Telegram 10817 (2017);

www.astronomerstelegram.org/?read=10817.27. R. Abbasi et al., Astrophys. J. 744, 1 (2012).28. J. Braun et al., Astropart. Phys. 29, 299–305 (2008).29. J. Braun et al., Astropart. Phys. 33, 175–181 (2010).30. See supplementary materials.31. K. Meagher, C. Raab, IceCube Collaboration, in 35th

International Cosmic Ray Conference, Proceedings of Science(2017); https://pos.sissa.it/301/957/pdf.

32. S. Paiano, R. Falomo, A. Treves, R. Scarpa, Astrophys. J. 854,L32 (2018).

33. M. Ackermann et al., Astrophys. J. 810, 14 (2015).34. M. G. Aartsen et al., Astrophys. J. 835, 45 (2017).35. M. Ackermann et al., Astrophys. J. 743, 171 (2011).36. S. S. Wilks, Ann. Math. Stat. 9, 60–62 (1938).

ACKNOWLEDGMENTS

Funding: We acknowledge support from the following agencies.United States:National Science Foundation (NSF) Office of PolarPrograms, NSF Physics Division, Wisconsin Alumni ResearchFoundation, Center for High Throughput Computing (CHTC) at theUniversity of Wisconsin–Madison, Open Science Grid (OSG),Extreme Science and Engineering Discovery Environment (XSEDE),U.S. Department of Energy National Energy Research ScientificComputing Center, particle astrophysics research computingcenter at the University of Maryland, Institute for Cyber-EnabledResearch at Michigan State University, and the astroparticlephysics computational facility at Marquette University. Belgium:Funds for Scientific Research (FRS-FNRS and FWO), FWOOdysseus and Big Science programmes, and Belgian FederalScience Policy Office (Belspo). Germany:Bundesministerium fürBildung und Forschung (BMBF), Deutsche Forschungsgemeinschaft(DFG), Helmholtz Alliance for Astroparticle Physics (HAP), Initiativeand Networking Fund of the Helmholtz Association, DeutschesElektronen Synchrotron (DESY), and High Performance Computingcluster of the RWTH Aachen. Sweden:Swedish ResearchCouncil, Swedish Polar Research Secretariat, Swedish NationalInfrastructure for Computing (SNIC), and Knut and AliceWallenberg Foundation. Australia:Australian Research Council.Canada:Natural Sciences and Engineering Research Council ofCanada, Calcul Québec, Compute Ontario, Canada Foundation forInnovation, WestGrid, and Compute Canada. Denmark:VillumFonden, Danish National Research Foundation (DNRF). NewZealand:Marsden Fund. Japan:Japan Society for Promotion ofScience (JSPS) and Institute for Global Prominent Research (IGPR)of Chiba University. Korea:National Research Foundation of


Fig. 4. Time-integrated analy-sis results. As in Fig. 3A, but forthe time-integrated analysis ofTXS 0506+056 using (A) the full9.5-year sample (2008–2017),and (B) the 7-year sample(2008–2015).




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be produced in the same processes that produceneutrinos—for example, when accelerated pro-tons interact with ambient lower-energy photonsnear the source, producing both neutral pions(which decay to gamma rays) and chargedpions (which decay to neutrinos and leptons). Ahigher luminosity in neutrinos than in gammarays could imply that a substantial fraction ofthe gamma rays related to the neutrino produc-tion are either absorbed or arriving at energiesabove or below the Fermi-LAT energy band.Although TXS 0506+056 is a bright object in

gamma rays, it was not previously singled out asa predicted neutrino source. In the third catalogof active galactic nuclei detected by Fermi-LAT(33) listing 1773 objects (including those at lowgalactic latitudes), TXS 0506+056 is among the50 brightest objects, with an average flux be-tween 1 GeV and 100 GeV of 6.5 (±0.2) × 10–9

photons cm–2 s–1. Its measured redshift nowmakes it one of themost luminous objects knownout to the same distance, more than an order ofmagnitude more luminous than nearby blazarssuch as Markarian 421, Markarian 501, and 1ES1959+650. With respect to these objects, animportant observational distinction is the fa-vorable declination of TXS 0506+056. As theneutrino-nucleon interaction cross section growswith energy, absorption in Earth becomes con-siderable for neutrinos above ~100 TeV. IceCubeis most sensitive to high-energy neutrinosfrom sources at declinations near the equatorialplane, which is viewed along the horizon fromthe South Pole. The blazars mentioned aboveare at more northern declinations, and the like-lihood that a neutrino with energy of ~300 TeVfrom one of these will be absorbed while travers-ing Earth is three to five times the likelihood thatit will reach the detector. The explanation forwhy TXS 0506+056 is the first blazar associatedwith a significant neutrino excess may there-fore depend on the combination of its intrinsicproperties and the observational properties ofthe detector.IceCube recently published (34) a search for

neutrino emission from the blazars in the secondcatalog of active galactic nuclei detected by Fermi-LAT (35), constraining their contribution to thediffuse astrophysical neutrino flux under different

model assumptions. An upper limit of 27% wasfound assuming the diffuse flux that is fit between10 TeV and 100 TeV with a soft E–2.5 spectrum(16). For an E–2 spectrum compatible with thediffuse flux fit above ~200 TeV (17), the upperlimit is between 40% and 80%. The allowed con-tribution by blazars as a population is larger, be-cause it would include the contribution of fainterand more distant blazars not yet resolved in thecatalog. Averaged over 9.5 years, the neutrino fluxof TXS 0506+056 by itself corresponds to 1% ofthe astrophysical diffuse flux and is fully com-patible with the previous blazar catalog results.The evidence presented above supports the

hypothesis presented in (20) that the blazar TXS0506+056 is a high-energy neutrino source. The3.5s evidence for neutrino emission during the5-month period in 2014–2015 is statistically in-dependent of the evidence presented in (20).The analysis of the IceCube-170922A event in(20) relies on correlation of a single neutrino withelectromagnetic activity, whereas the analysispresented here relies only on self-correlationof multiple neutrinos. The coincidence of anIceCube alert with a flaring blazar, combinedwith a neutrino flare from the same object inarchival IceCube data, pinpoints a likely sourceof high-energy cosmic rays.

REFERENCES AND NOTES

1. Pierre Auger Collaboration, Science 357, 1266–1270(2017).

2. F. Reines, Annu. Rev. Nucl. Part. Sci. 10, 1–26 (1960).3. C. M. Urry, P. Padovani, Publ. Astron. Soc. Pac. 107, 803

(1995).4. K. Mannheim, Astropart. Phys. 3, 295–302 (1995).5. F. Halzen, E. Zas, Astrophys. J. 488, 669–674 (1997).6. A. Mücke, R. J. Protheroe, R. Engel, J. P. Rachen, T. Stanev,

Astropart. Phys. 18, 593–613 (2003).7. K. Murase, in Neutrino Astronomy, T. Gaisser, A. Karle, Eds.

(World Scientific, 2017), pp. 15–31.8. M. Petropoulou, C. D. Dermer, Astrophys. J. Lett. 825, L11

(2017).9. C. Guépin, K. Kotera, Astron. Astrophys. 603, A76 (2017).10. M.-H. Ulrich, L. Maraschi, C. M. Urry, Annu. Rev. Astron.

Astrophys. 35, 445–502 (1997).11. M. G. Aartsen et al., J. Instrum. 12, P03012 (2017).12. M. G. Aartsen et al., Astrophys. J. 835, 151 (2017).13. M. G. Aartsen et al., Phys. Rev. D 89, 102004 (2014).14. IceCube Collaboration, Science 342, 1242856 (2013).15. M. G. Aartsen et al., Phys. Rev. Lett. 113, 101101 (2014).16. M. G. Aartsen et al., Astrophys. J. 809, 98 (2015).17. M. G. Aartsen et al., Astrophys. J. 833, 3 (2016).

18. M. G. Aartsen et al., Astrophys. J. 807, 46 (2015).19. E. Massaro et al., Astrophys. Space Sci. 357, 75 (2015).20. IceCube, Fermi-LAT, MAGIC, AGILE, ASAS-SN, HAWC, H.E.S.S.,

INTEGRAL, Kanata, Kiso, Kapteyn, Liverpool Telescope, Subaru,Swift/NuSTAR, VERITAS, and VLA/17B-403 teams, Science361, eaat1378 (2018).

21. M. G. Aartsen et al., Astropart. Phys. 92, 30–41 (2017).22. IceCube Collaboration, GRB Coordinates Network, Circular Service

21916 (2017); https://gcn.gsfc.nasa.gov/gcn3/21916.gcn3.23. Y. T. Tanaka, S. Buson, D. Kocevski, Astronomer’s

Telegram 10791 (2017); www.astronomerstelegram.org/?read=10791.

24. W. B. Atwood et al., Astrophys. J. 697, 1071–1102 (2009).25. J. Aleksić et al., Astropart. Phys. 35, 435–448 (2012).26. R. Mirzoyan, Astronomer’s Telegram 10817 (2017);

www.astronomerstelegram.org/?read=10817.27. R. Abbasi et al., Astrophys. J. 744, 1 (2012).28. J. Braun et al., Astropart. Phys. 29, 299–305 (2008).29. J. Braun et al., Astropart. Phys. 33, 175–181 (2010).30. See supplementary materials.31. K. Meagher, C. Raab, IceCube Collaboration, in 35th

International Cosmic Ray Conference, Proceedings of Science(2017); https://pos.sissa.it/301/957/pdf.

32. S. Paiano, R. Falomo, A. Treves, R. Scarpa, Astrophys. J. 854,L32 (2018).

33. M. Ackermann et al., Astrophys. J. 810, 14 (2015).34. M. G. Aartsen et al., Astrophys. J. 835, 45 (2017).35. M. Ackermann et al., Astrophys. J. 743, 171 (2011).36. S. S. Wilks, Ann. Math. Stat. 9, 60–62 (1938).

ACKNOWLEDGMENTS

Funding: We acknowledge support from the following agencies.United States:National Science Foundation (NSF) Office of PolarPrograms, NSF Physics Division, Wisconsin Alumni ResearchFoundation, Center for High Throughput Computing (CHTC) at theUniversity of Wisconsin–Madison, Open Science Grid (OSG),Extreme Science and Engineering Discovery Environment (XSEDE),U.S. Department of Energy National Energy Research ScientificComputing Center, particle astrophysics research computingcenter at the University of Maryland, Institute for Cyber-EnabledResearch at Michigan State University, and the astroparticlephysics computational facility at Marquette University. Belgium:Funds for Scientific Research (FRS-FNRS and FWO), FWOOdysseus and Big Science programmes, and Belgian FederalScience Policy Office (Belspo). Germany:Bundesministerium fürBildung und Forschung (BMBF), Deutsche Forschungsgemeinschaft(DFG), Helmholtz Alliance for Astroparticle Physics (HAP), Initiativeand Networking Fund of the Helmholtz Association, DeutschesElektronen Synchrotron (DESY), and High Performance Computingcluster of the RWTH Aachen. Sweden:Swedish ResearchCouncil, Swedish Polar Research Secretariat, Swedish NationalInfrastructure for Computing (SNIC), and Knut and AliceWallenberg Foundation. Australia:Australian Research Council.Canada:Natural Sciences and Engineering Research Council ofCanada, Calcul Québec, Compute Ontario, Canada Foundation forInnovation, WestGrid, and Compute Canada. Denmark:VillumFonden, Danish National Research Foundation (DNRF). NewZealand:Marsden Fund. Japan:Japan Society for Promotion ofScience (JSPS) and Institute for Global Prominent Research (IGPR)of Chiba University. Korea:National Research Foundation of


Fig. 4. Time-integrated analy-sis results. As in Fig. 3A, but forthe time-integrated analysis ofTXS 0506+056 using (A) the full9.5-year sample (2008–2017),and (B) the 7-year sample(2008–2015).




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7 years

9.5 years


• Observed luminosities in gamma-ray and neutrino are different• Neutrino luminosity ~ 1.2e47 erg s^-1 during 158 days• Gamma-ray luminosity ~ 0.28e47 erg s^-1 during the same period

of time ~ similar to the long-term luminosity between 0.1 and 100 GeV

• Uniqueness of TXS 0506+056• Gamma-ray bright• Location with respect to IceCube

Documents

Neutrino emission from the direction of the blazar TXS 0506+056 …sirius.unist.ac.kr/SRC-CHEA/presentations/2018+2nd+jc... · 2018. 9. 21. · the electromagnetic emission can be