光赤外線大学間連携 OISTER によるマルチメッセンジャー天文学
村田勝寛, 太田耕司, 野上大作（京都大学）, 高橋幸弘, 齊藤大晶（北海道大学）, 大朝由美子（埼玉大学）, 土居守, 瀧田怜（東京大学）, 谷津陽一,高橋一郎（東京工業大学）, 金田英宏, 楠根貴成（名古屋大学）, 伊藤洋一, 高橋隼（兵庫県立大学）, 川端弘治, 中岡竜也（広島大学）,永山貴宏（鹿児島大学）, 泉浦秀行, 花山秀和, 早津夏己（国立天文台）, 光赤外線大学間連携 OISTER
光赤外線大学連携 OISTERは、日本の9大学と国立天文台が国内外の可視光・赤外線望遠鏡を有機的に結びつけ、突発天体・現象に即応した多波長・多モード同時観測を実現し、また、各大学のみでは実現困難な人材育成をおこなうプロジェクトである。2022年度から始まった第3期では、マルチメッセンジャー天文学や時間領域天文学を含む幅広い研究を進めている。OISTERに参加する望遠鏡は、これまでにも、重力波イベントGW170817の観測や、高エネルギーニュートリノ事象IceCube-170922Aの電磁波対応天体の捜索に参加し、成功を収めてきた。また、ガンマ線バーストや超新星爆発など、重力波・高エネルギーニュートリノ事象と関連が予想される天体の観測にも積極的に取り組んでおり、成果を上げてきている。例えば、GRB 211211A
は、継続時間が長いガンマ線バーストでありながら、紫外線から近赤外線の放射はコンパクト天体の合体によるキロノバ現象によって説明されうる特異な天体（Troja et al. 2022）だが、この成果にも、OISTERの観測が貢献している。今後も、重力波・高エネルギーニュートリノ事象の可視光・赤外線対応天体のフォローアップ観測と、関連した天体の観測を進めることで、重力波源の多様性の解明、天体合体プロセスの物理の解明、rプロセス元素の起源の解明や、高エネルギーニュートリノ源やその発生プロセスの解明を目指していく。

Telescopes of the OISTER

Observational Targets of the OISTER1⑥ U of Hyogo
Nayuta⑦ Kyoto UMITSuME Okayama

2.0m

0.5m

① Hokkaido U⑤ Kyoto U
0.4m telescope⑨ Hiroshima U
Kanata

Focusing on the multi-messenger astronomy and time-domain astronomy, we haveobserved various targets including gravitational waves, neutrino events, supernovae,flare stars, dwarf novae, X-ray binaries, AGNs, GRBs, exoplanets, Solar systemobjects, pre-main-sequence stars.

Pirka
1.6m

⑧ Kyoto U
Seimei

1.5m

3.8m② Saitama U
SaCRA

3９ 8,７⑩ Kagoshima U
1.0m telescope６4

20.55m510③ UTokyo
Kiso S

Fig. 2 Wide variety of objects for the OISTER observations (left) and1.05m

white papers published in 2021 (right).

South Africa

X線連星⑪ NAOJ
Murikabushi

11Nagoya U
IRSF1.4m

1.05m④ Tokyo TechMITSuME Akeno
0.5m

Fig. 1 Observatories operated by the OISTER (9 universities and NAOJ)
Fig. 4 Number of theMulti-Messenger Astronomy: Follow-up
Observations of Gravitational Waves
Many telescopes of the OISTER are participating in the Japanese collaboration
for Gravitational-wave Electro-Magnetic follow-up, J-GEM, conducting opticaland infrared follow-up observations of gravitational waves (GWs).

Follow-up Observations of GW170817
The J-GEM observed AT2017gfo/SSS17a, the optical counterpart ofGW170817, which was caused by abinary neutron star (BNS) merger andresulted in the only optical counterpart
observed to date.
The observed light curve can beunderstood by kilonova model.
The near-infrared data were mainly
taken by the IRSF telescopein Sutherland, South Africa,
participating in the OISTER.

Utsumi et al. 2017

Fig. 3 Number of the OISTER
observations

Follow-up Observations of GRB211211A
Troja et al. 2022

Some of the OISTER telescopes are
conducting immediate observations of GRBs.
The MITSuME Akeno 50cm telescopeobserved GRB 211211A starting 0.24 days
after the Fermi trigger (GCNC #31217).
Despite the long duration of GRB211211A,
observations in ultraviolet to near-infrared
suggest that it can be explained by akilonova from the merger of compact objects(Troja et al. 2022, Nature, 612, 228). The
MITSuME contributed to this result throughFig.5 Multicolor light curves
compared to models’ predictions of a optical observations.
kilonova (solid line) in addition to the
non-thermal emission (dashed line).

Educational Activities

Fig. 6 Light curve of the optical counterpart56” x 56”
optical z band: Subaru/HSC
near-infrared H, Ks band: IRSF telescope
Utsumi et al. 2017

Fig. 7 Three-color composite images from the J-GEM observations

Follow-up Observations during the LIGO-Virgo O3 run

Sasada et al. (2021)

Fig. 8 Limiting magnitudes of the J-GEM
observation during O3.
The lines are expected magnitudes ofoptical counterpart at 100 Mpc.

refereed papers resulting
from the OISTER projectsTelescopes of the OISTER
conducted observations ofcandidate galaxies within the GW
error region through the J-GEM.
During O3, the J-GEM observed
23 GW events, focusing on NS+NS
and NS+BH(NS: neutron star , BH:
black hole), where electromagnetic
waves are expected.
At most, 170 galaxies wereobserved in a single event,S190425z.
Observations for GWs within 100
Mpc can be expected to result indetection
Observations are also ongoing
during the O4 run.

To nurture highly-skilled youths by offering opportunities for undergraduate/master/Ph.D. students and Postdocs to engage in not only extensive science activities but
also productive educational programs including on-site observations andinstrumentation experiences. We have been conducting a variety of educational
programs such as short-term stay training, workshops, and various seminars.

Short-Term Stay Training Program
Objective: Skill enhancement for students and researchers. Developing individuals
who utilize their expertise while possessing a broad perspective and thinking abilities.
Target: Graduate students and Postdocs affiliated with OISTER institutions, who areengaged in research in the optical and infrared observational astronomy.
Support Details:
Travel expenses provided for the stay, limited to the domestic travel
Basic instruction related to observation and analysis, and equipment and systemdevelopment
Duration of Stay: Several days to about one week.
Number of implementations: 21 cases from 2013FY to 2022FY
Spectroscopy: 9, Equipment & System Development: 5,Polarimetry: 3, Imaging: 4

Number of the degree holders related to the OISTER

Fig. 9