すばる等によるIceCube イベントのfollow-u
Optical and Near-Infrared Follow-up observations
for IceCube eventswith Subaru/8m-class telescopes
太田耕司（京大）、諸隈智貴 (東大)K. Ohta (Kyoto)、T. Morokuma(Tokyo)

マルチメッセンジャー天文学研究会２０１８
2018年3月26-27日 千葉大学

Contents
possible origins of high-energy neutrinos / highenergy cosmic ray
counterpart search strategy in opticalnew BLAZAR catalog (BROS)
flowchart for optical follow-up w/8-10m classtelescopes
e.g., 170922A
summary & future prospects2

Origin of high-energy (T-PeV) neutrinos(high-energy cosmic ray)©NASA/Fermi©U. Tokyo(peculiar) supernova

blazar: AGN relativistic jet©NASA©NSF

GRB

starburst galaxy3

EM Counterpart Search of IceCube events
Typically ~0.5-0.8 deg localization (EHE)
O(103) transients@optical w/Subaru(T. Morokuma+2008, M. Yoshida+2017)

Case for IceCube 170922A

1 deg

5

Possible candidates
in an error region of an IceCube event•Starburst galaxies~<30%@100 TeV(Bechtol+2017)

so many star-forming
galaxies ・・・
transient in optical light?
Can we identify it?
almost impossible?

•GRBs
time coincidence
small error region
afterglowWe may be able toidentify itBut virtually no suchcases<1% (Aartsen+2017)
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Possible candidates
in an error region of an IceCube event•SuperNovae
so many SNe・・・
peculiar SN?
(2012Mar SNIIn z=0.07,Aartsen+2015)

Peculiar light curve,spectrum?
Can we identify it?
might be?

•BLAZARsseveral BLAZARs in the error
regionflaring up?
We already identify it?
IC35(121204):flaringFSRQ@z=1.5(?)
170922A:flaring BL Lac@z=0.3

We need to accumulate
such cases7

A strategy to make optical follow-up
w/8-10m class telescopes• Machine time of 8-10m class telescopes is very much tight• many SNe, star-burst galaxies, AGNs in the error region=> almost impossible to identify the optical counterpart…
• Some strategy is necessary
GW source:
search for NS-NS (or NS-BH) model–like object
IceCube event: search for BLAZAR?
even if the BLAZAR population is not the majority (~<27 %,Fermi, Aartsen+2017) population,accumulation of such follow-up observations would benecessary in the early phase of the follow-up observation
study8Search for flaring BLAZARBLAZAR catalogs
・Fermi-LAT 3FGL (2015) ~1100 BLAZARs(BL & FSRQ)
・5th ROMA-BZCAT (2015) ~3500
・Flat spectrum radios sources (α>-0.5, fν∝να）
BLAZAR candidate catalogs (CLASS, CRATES)CRATES : Healey et al. 2007
4.8GHz GB6 etc >65mJy 0< δ < 75°|b|>10°
1.4GHz NVSS > 2.5 mJy=> 11,131 sources
9A New Blazar Catalog (BROS)
Blazar Radio and Optical Survey (BROS; Itoh et al. in prep.)
TGSS 0.15 GHz rms~3.5mJy/beam >10-20mJy (Intema+2017)
recent sky survey w/GMRTNVSS 1.4 GHz > 2.5 mJy (Condon+1998)
Flat spectrum sources α>-0.5 (fν∝να）
56,315 sources at Dec.>-40 deg
Pan-STARSS(PS1)@optical~40% not detected in PS1 (r>23)

10

BROS:
Deeper catalog of flat radio sources
Flux density (mJy)

65

10-20GB6TGSS

CRATES

BROS

NVSS

2.5
0.1

101Frequency (GHz)11

Optical properties of BROS sources

optical magnitude (g-mag) => bright

BLAZAR sequence

New sequence?

blue <= optical color (g-r) => red12

New sequence?
Thanks to the deeper flux limit at 1.4GHz?
Most of the new sequence sources show a 1.4GHz fluxdensity < 65 mJy.
Elliptical galaxies (both in color and morphology)
Optical spectroscopy for a few of them with 4m(Mayall)
does not show strong emission lines (BL Lac like?).
Good news for nearby TeV source search (?)

BROS

CRATES13

Counterpart Search Strategy@optical14

Case for IceCube 170922A

w/Kanata 1.5m

15

Road to EM Counterpart Discovery of IceCube-170922A
IceCube alert (GCN 21916): 2017/09/22, 20:54:30 (UT)
7 BROS sources within IceCube-170922A error region
We observed all of them w/ Kanata/HONIR on 2017/09/24
TXS 0506+056 variability detected

2MASSより増光か？

Kanata/HONIR FoV

Kanata/HONIR J-band16

Road to EM Counterpart Discovery of IceCube-170922A
TXS 0506+056 variability detected with Kanata/HONIR on 2017/09/24=> found Fermi/LAT (gamma, ATel #10791, Tanaka+),
ASAS-SN (optical) variabilities==> multi-wavelength follow-up
optical/NIR imaging, spectroscopy, polarization: incl. MITSuME, Kiso, Nayuta,Kanata, IRSF (OISTER) + Subaru (T. Morokuma+ in prep.)
Fermi・LAT(0.8-10 GeV)

ASAS-SN long-term light curve (V-band)
1,000 days

3/23

1 yr2MASS

3/23 - 3/24
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w/Kanata 1.5m,
Nayuta 2m

19

redshift of TXS 0506+056

PS1 (gri)2.5 arcmin

BL Lac? ~ 15 mag
z=0.336 (Ajello+2014) ??
z>0.21 (Shaw+2013)
no reliable determination?
8m-class telescopes are necessary “in general”. (e.g., Landoni+2015)
new observations
Kanata (1.5m)
KanataNayutaNayuta (2m)Liverpool (2m)=>
Subaru/FOCAS (8.2m,~12min)Gemini-N/GMOS (8.2m)
SALT/HRS (10m, 2500 sec), VLT/X-Shooter (8.2m, 30 min)
GTC/OSIRIS (10m,10h)21

Optical Spectroscopy: redshift determination

0.1-0.3 hour integration
Subaru(8.2m)/FOCAS
S/N~100

1% (S/N=100)

Paiano+2018 (background)23

Optical Spectroscopy: redshift determination
0.1-0.3hour integration
Subaru(8.2m)/FOCAS
S/N~100
10-hour integration
GTC(10m)/OSIRIS
S/N~500
50 times longer
1.5 times larger==> ~9 times better
than Subaru/FOCAS
1% (S/N=100)

Paiano+2018

z=0.336 < 0.4
consistent w/ MAGIC highenergy gamma detection24

In case of a faint BROS source

FSRQ => OK, if not sofaintBL Lac => mmm…

25

In case of no flaring BROS source
Search for faint BLAZAR,
peculiar SN,
its follow-up spectroscopy?

26

Summary & Future Prospects
Several mechanisms proposed for high-energy neutrinos
Still hard to identify the optical counterpart
So here we mainly target on BLAZARs
We developed a new blazar catalog (flat-spectrum radiosources: BROS) incl. ~56,000 sources
Our Kanata quick follow-up for BROS sources foundvariability of TXS 0506+056==> Fermi/LAT variability ==> further follow-ups
10-hour integration w/ 10m telescope GTC determines theredshift z=0.336 (S/N~several hundreds for BL Lac)
For future IceCube alerts, we need multiple/coordinatedobserving strategies w/ small (OISTER) & large (Subaru etc.)
telescopes27以下は予備28

Other future task
• Positional coincidence (expected number)• Time coincidence within Δt (but what Δt ?)• Probability of L > <L>+ΔL : P(ΔL) (time scale?)• Probability of polari > <polari> + Δpolari29Gammaray(FermiLAT)

IC35(HESE-35、BigBird)

Radio(8.4GHz)
30