Fermi-LAT detection of a ﬂaring blazar
inside the error region ofIceCube-170922A

Yasuyuki Tanaka (Hiroshima University)

Outline• Motivation: why we perform IceCube follow-up• Current status of Fermi Gamma-ray Space Telescope• Fermi-LAT detection of a ﬂaring blazar, TXS 0506+056,

inside the error region of IceCube-170922A• Multi-wavelength light curves and SED of TXS

0506+056• SummaryMotivation: Understanding the origin ofcosmic rays

Radiation measure experiment by Hess
©ICRR
Cosmic-ray spectrum
measured on the Earth•Highest-energy cosmic rays reach 1020 eV and the spectrum isrepresented by power-law shape•

Long-standing problem since its ﬁrst discovery in 1912 is where and how
cosmic rays are produced

Active Galactic Nucleus Jets
•Jets are ejected from supermassive (108-1010M̲sun) blackholeand particles are accelerated inside the jets
Radio image of Cygnus A

AGN jets are considered to be oneof the promising candidates ofcosmic-ray source©NRAO

AGN jetUrry+95
Particles are accelerated by shocks
inside the jet

Unveiling the source of cosmic rays throughIdentifying the IceCube neutrino source
New era of Muliti-messenger astronomy
High-energy neutrinos are produced via
interaction between cosmic rays andambiend photons (pγ) or protons (pp)Neutrino source＝Cosmic-ray source
Neutrino arrival direction
indicates the direction of

taken from IceCube webpage

cosmic-ray sources• 54 events during the ﬁrst 4-year operation• Isotropic distribution implies extragalactic

origin• Alert is issued via GCN since 2016 Apriltaken from ICRC 2015 proc.

Outline• Motivation• Current status of Fermi Gamma-ray Space

Telescope• Fermi-LAT detection of a ﬂaring blazar, TXS 0506+056,

inside the error region of IceCube-170922A• Multi-wavelength light curves and SED of TXS0506+056• SummaryFermi Gamma-ray Space Telescope• Launched on 2008 June 11• Continue to observe without any
critical problems• All sky survey mode
Large Area Telescope (LAT)- 20 MeV-300 GeV- Thanks to the wide FoV of 2.4 str, scan all-sky every 3 hours

Gamma-ray Burst Monitor (GBM)- 8 keV-40 MeV- all-skyLarge Area Telescopeγ

Pair-conversion telescope

ACDTracker

Si-strip Tracker with tungsten foil converter:
Measure the photon directionCsI Calorimeter: Measure the photon energy,
Image the shower
ACD (Plastic scintillator):
Reject charged-particle background

••
•
•
•

Large effective area (9000 cm2 @ 1 GeV,normal incidence)
Large field-of-view (2.4 str)
The entire sky is observed every ~3 hours
Energy range: 20 MeV – 300 GeV
Angular resolution (68% contaminant radius):
0.6 deg @ 1 GeV

e+ eCsI Calorimeter4 x 4 modular array
3000 kg, 650 W

Energy resolution and PSF• 12 layer (FRONT)• 4 layers (BACK)
https://www.slac.stanford.edu/exp/glast/groups/canda/lat_Performance.htm

All-sky survey-mode observation• Thanks to the large FoV of 2.4 str, LAT scans all-sky every 3
hours (i.e., 2 orbits) and perform unbiased survey

3FGL catalog from 4-year data

(http://fermi.gsfc.nasa.gov/ssc/data/access/lat/4yr_catalog/)• Arxiv: 1501.02003• 3033 sources with TS>25 (~5sigma) detection• 992 sources are unID
• GeV spectra and 4-year light

curves are available for all thesources from webpage

3LAC (LAT AGN Catalog)

Ackermann+15• 467 FSRQs• 632 BL Lacs
• 460 Uncertain type• 32 non-blazar AGN

Confirmation of Blazar sequence• FSRQ: strong optical emission lines due
to bright accretion disk

• BL Lac: weak/no lines (EW<5A)• Blazar sequence: Bright/faint blazars
have lower/higher sync. peak freq.

Fossati+98
Kubo+98

LAT Automated Science Processing (ASP)+Flare advocate
LAT
1-daydata• Flare Advocate run the daily (1-day and 6-hour data) analysis script andcheck the ASP result• Once transient objects are found, Astronomers Telegram is issued(typically, flux >1.0x10-6 photons/cm2/s for E>100 MeV)• LAT daily report is uploaded on
the confluence page(collaboration member only)• 24-hour, 6-hour x4

Fermi All sky Variability Analysis (FAVA)• For Weekly-binned data
• Comparison of observed counts withaverage (expected) counts• E>100 MeV, E>800 MeV• Crab nebula flare is first detected bythis analysis• By using 47 month Fermi/LAT data,

215 sources in the first flare catalog(FAVA catalog paper)

Exposure ratioFAVA webpage• https://fermi.gsfc.nasa.gov/ssc/data/access/lat/FAVA/LightCurve.php• Automatic production of light curve at any locations (RA, Dec)

IceCube-161210• At the IceCube trigger time, theevent position is outside LAT FoV• No LAT emission by LTF• TS maps by manual analysis foundweak sources at the edge of theIceCube error circle??

• Probably statistical fluctuation
TSmap for T0-24h~T0

Produced by Burst
Advocate tool

T0~T0+24h

Possible association of PeV neutrino withhigh fluence GeV blazar PKS 1424-418

Cascade event oferror radius of ~10 deg~5% chance probability

Kadler+16

Outline• Motivation• Current status of Fermi Gamma-ray Space Telescope• Fermi-LAT detection of a ﬂaring blazar, TXS

0506+056, inside the error region ofIceCube-170922A• Multi-wavelength light curves and SED of TXS

0506+056• Summary

IceCube-170922A•

JST 2017/9/23 5:55AM: GCN notice is issued•

10:09AM: Oﬄine analysis result is issued (GCN 21916)

EHE alertFermi-LAT detection of a ﬂaring blazar TXS 0506+056
inside the error region of IceCube-170922A
Fermi-LAT count map
FAVA (E>800 MeV) light curve

T0-4.2m~T0

T0-8.4m~T0-4.2m

Flaring blazar, TXS 0506+056 wasdetected inside the IceCube-170922A
error region(Tanaka et al. ATel #10791)

MAGIC sub-TeV gamma-ray detection
from TXS 0506+056

ASAS-SN optical V-band light curve andpolarization measurement by Kanata/HONIR•

IceCube trigger time corresponds to the brightest
phase in the optical band, indicating the possible
association with IceCube neutrino and this ﬂaring
blazar•Signiﬁcant polarization (~6% PD) was detected(interstellar polarization is <1%)

Polarization Degree [%]IceCube trigger (MJD 58018.87)
Polarization Angle [deg]Subaru/FOCAS spectroscopy(Morokuma+, ATel #10890)
Subaru/FOCAS follow-up to measure the redshift

TXS 0506

Featureless(redshift isstill unknown)

Nearby star

Foregroundsky emission

Summary• Fermi-LAT detected a ﬂaring blazar, TXS 0506+056, inside the error
region of IceCube-170922A• MAGIC also detected sub-TeV emission from TXS 0506+056, supporting
the possible association between the IceCube neutrino and the blazar• The neutrino ﬂux is comparable to GeV-TeV gamma-ray ﬂux, further
supporting the association• Multi-wavelength follow-ups were triggered after the Fermi-LAT detection• We have also performed optical ToO observation toward this blazar withKanata/HONIR, Kiso/KWFC, Subaru/HSC, FOCAS etc• Redshift is still unclear• CTA-LST follow-up for IceCube alert is deﬁnitely important to discover
the second blazar association