Gemini Gravitational-wave Source Follow-up Program

Gregory S-H Paek¹, Hyeonho Choi¹, Ji-Hoon Kim¹, Seowon Chang¹, Mankeun Jeong¹, Chung-Uk Lee², Seung-Lee Kim², Hyun-Il Sung², Joonho Kim³, David Buckley⁴, Hyung Mok Lee¹, Hongjae Moon¹, and KS4/7DS/GECKO Team

K-GMT Science Users Meeting (KASI, Dajeon)

1

2024/08/21 - 08/23

1. Seoul National University, 2. KASI, 3. DNSM, 4. SAAO

Myungshin Im

(Seoul National University)

2024-08-21

We are now exploring the universe with something other than the light

• Electromagnetic wave (EM)

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• Gravitatioanl-wave (GW)

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• Neutrinos

K-GMT Science Users Meeting (KASI, Dajeon)

2

2024/08/21 - 08/23

LIGO/Virgo GW Observatories

Hundreds of black hole mergers, events have been identified since 2015, but …

Solar Masses

Limitations of GW Astronomy

• Black hole mergers 🡺 no light

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• Poor localization with GW alone: do not know exactly where the GW event occurred

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• Limited usefulness of GW events for many astrophysical applications (cosmology, heavy element production, etc)

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K-GMT Science Users Meeting (KASI, Dajeon)

3

2024/08/21 - 08/23

GW150914 (600 deg²)

Hubble Tension: Different methods gives different H₀ values

K-GMT Science Users Meeting (KASI, Dajeon)

4

2024/08/21 - 08/23

A few % accuracy Ho measure

An independent method of measuring distance is necessary 🡺 GW MMA

• GW: Luminosity distance

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• EM: Redshift

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K-GMT Science Users Meeting (KASI, Dajeon)

5

2024/08/21 - 08/23

A few % accuracy Ho measure

Binary Neutron Star (BNS)/�Neutron Star-Black hole (NSBH) Mergers

• Produces debris that can emit electromagnetic wave (EM; light) 🡺 Kilonova (KNe), short GRBs, …

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• Finding KNe accompanying GW events is a key for the success of MMA 🡺 Location & Environment, Redshift, etc

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K-GMT Science Users Meeting (KASI, Dajeon)

6

2024/08/21 - 08/23

Current difficulties In MMA

• Search aera is too wide (~100 deg² or more)

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• KNe: Faint, fast-decaying transient (> 20 mag)

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• Too many other tranients (10-100/deg²)

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K-GMT Science Users Meeting (KASI, Dajeon)

7

2024/08/21 - 08/23

Important to find kilnova fast

(1-2 days)

Brightness

Days

KN

SNe

GW EM Counterpart Korean Observatory (GECKO)

K-GMT Science Users Meeting (KASI, Dajeon)

8

2024/08/21 - 08/23

Australia: LSGT 0.43m (SSO), KMTNet

US: LOAO 1-m

Uzbekistan:MAO 1.5m

Korea: SNU 1.0m,

DOAO 1.0m, CBNUO 0.6m,

KHAO 0.8m, 0.4m

US: McDonald

2.1-m, 0.8m, 0.25m

Chile: Gemini-S, KMTNet, KCT/RASA36 (0.4m), 7DT

Hawaii: Gemini-N

KMTNet 1.6m

Yellow: Spectroscopy

Light yellow: medium-band

South Africa,

Australia,

Chile

7-Dimensional Telescope (7DT)�- 20, 0.5m wide-field telescope�- Each telescope cover two different wavelengths�- Wide-field spectral mapper (R ~ 40)

K-GMT Science Users Meeting (KASI, Dajeon)

9

2024/08/21 - 08/23

7DT in construnction (2023-10)

Chile, El Sauce Observatory

Search for KN

K-GMT Science Users Meeting (KASI, Dajeon)

10

2024/08/21 - 08/23

GW Alert

Imaging Observations

(~a few 100,000 sources per field)

Transient search

Spectroscopy and

KN identification

Time series follow-up

Our strategy

• Find the EM counterparts (KNe) of GW events with GECKO

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• Tiling observation
• Galaxy-target observation

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• Search for new transients & pick promising candidates

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• Use Gemini to confirm their nature and redshifts

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K-GMT Science Users Meeting (KASI, Dajeon)

11

2024/08/21 - 08/23

GW Observing Run O4b: 2024/8 – 2025/7

• 10(+52-10) BNS/NSBH events in O4 (original) 🡺 1-3 in O4b?
• Median localization of 33 deg²

K-GMT Science Users Meeting (KASI, Dajeon)

12

2024/08/21 - 08/23

Our Gemini program (2024B)

• Target-of-Opportunity program

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• 4.5 hrs (GS) + 4.5 hrs (GN)

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• Imaging: GMOS-N, GMOS-S

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• Optical spectroscopy: GMOS-N, GMOS-S

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• NIR Imaging: GNIRS, FLAMINGOS2

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• NIR Spectroscopy: GNIRS, FLAMINGOS2

K-GMT Science Users Meeting (KASI, Dajeon)

13

2024/08/21 - 08/23

Binary neutron star merger event, GW170817, marked the start of multi-messenger astronomy

K-GMT Science Users Meeting (KASI, Dajeon)

14

2024/08/21 - 08/23

GW

Gamma-ray

+2sec

UV/Optical/NIR

+11hrs

X-ray

+9days

Radio

+16 days

KMTNet@SAAO

Imaging (Optical+NIR)

• Confirm the transient nature (R > 21-22 mag at 200 – 300 Mpc)
• Follow the long-term light-curve evolution to characterize KN property

K-GMT Science Users Meeting (KASI, Dajeon)

15

2024/08/21 - 08/23

Spectroscopy

• Confirm KN nature of the transient

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• Determine redshift of the event

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• Compare with model predictions and determine heavy element abundance

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K-GMT Science Users Meeting (KASI, Dajeon)

16

2024/08/21 - 08/23

KN Identification

• With spectrum, KN can be easily distinguished from other transients with similar photometric colors

K-GMT Science Users Meeting (KASI, Dajeon)

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2024/08/21 - 08/23

What heavy elements produced?

• Optical/NIR spectra 🡺 Lanthanide elements can be identified

K-GMT Science Users Meeting (KASI, Dajeon)

18

2024/08/21 - 08/23

Domoto+23

S240422ed

• NSBH event
• 90% area: 259 deg2
• Distance: 188+-43 Mpc

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• KMTNet R-band imaging to 20.4 – 22.4 AB mag depths (5-sigma)

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• 10s of candidate transients were identified

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KMTNet Coverage of S240422ed

Optical Transients in S240422ed Field

• Early light curves show GECKO24a is the most promising

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• SALT spectrum, obtained (courtesy of D. Buckley)

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• But the host seems too far, and long term light curve does not follow the expected trend

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GECKO24a

GECKO24a

Science

Reference

Difference

GW Observation Horizons in 2020s and 2030s

• Currently, BNS merger rate of 1/yr at D < 200 Mpc

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• In future, 100s of such events out to 10,000 Mpc or more

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• Future is bright for GW-EM MMA, but follow-up facilities must be in place

K-GMT Science Users Meeting (KASI, Dajeon)

21

2024/08/21 - 08/23

Redshift

Current

Future

BNS merger

BBH

mergers

Bailes+21

Concluding Remark

• GW O4b run can possibly find a few BNS or NSBH events

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• GECKO will identify them

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• Gemini will confirm them and characterize them

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• GW MMA will flourish in years to come, and this project will be an important stepping stone for the future efforts

K-GMT Science Users Meeting (KASI, Dajeon)

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2024/08/21 - 08/23