​

Observation of electromagnetic

counterparts of GW events

• Biswajit Banerjee

GW 170817/ GRB 170817A

A. Stamerra, O. S. Salafia, D. Miceli and C. Righi, ICRC 2021

GW 170817/ GRB 170817A

A. Stamerra, O. S. Salafia, D. Miceli and C. Righi, ICRC 2021

GeV TeV

Less known

territory in transients

4

Ongoing observation run of LVK: O4

O4 volume ~ 3*O3 volume

O5 volume ~10*O3 volume

Abbott et al. 2020, LRR

No BNS in O4

5

GRB 211211A: long GRB/ KILONOVA

Minute-duration GRB, prompt and bright spikes last more than 12 s

​

Nearby GRB at 350 Mpc and 7.9 kpc from the galaxy center

Rastinejad, J. C. et al. 2022 Nature

6

GRB 211211A: GeV emission

Discovery of a significant

(>6σ) transient-like emission by Fermi/LAT

​

Photon energies 0.1-1 GeV

Mei, BB, Oganesyan et al. 2022, Nature

• ​

​

• GW170817-like events are within reach

​

See also Troja et al. 2022 Nature, Xiao, S. et al. 2022 Nature, Rastinejad, J. C. et al. 2022 Nature

​

GRBs in VHE gamma-rays; > 2019

7

GRB 190114C

GRB 180720B

• Acciari et al 2019, Nature

Abdalla et al 2019, Nature

GRB 221009A; BOAT (Brightest Of All Time^*)

z~ 0.15

LHAASO Collaboration,

Science (2023)

z~ 0.15

LHAASO Collaboration,

Science (2023)

Discovery of “Ravasio line”: Ravasio et al. 2024, Science

GRB 221009A; BOAT (Brightest Of All Time)

Nature of the early GeV emission

10

• For some GRBs early GeV emission follows variability of prompt

Zhang et al. 2011

​

​

• Early Afterglow or Prompt origin?

Ghisellini et al. 2009,

Kumar & Barniol Duran, 2009

Maxham et al. 2011

​

​

• What is the contribution of the keV-MeV prompt?

​

​

• Prompt second component?

Time since GBM Trigger (s)

Macera et al 2025 (A&A)

GRB 221023A

Results of the time-resolved spectral analysis

11

Sample divided in two groups

High-Energy emission dominated by synchrotron

High-Energy emission dominated by

power law

1

2

See also

Ravasio et al 2023

GRB 221023A

GRB 090902B

Cherenkov Telescope Array Observatory (CTAO)

1. Largest ground-based Cherenkov telescope, >100 telescopes with two proposed sites: La Palma, Spain and Chile.
2. 10X sensitivity than MAGIC, HESS.
3. Operational energy range: 0.01-100 TeV
4. Field of view up to ~50 sq. deg.
5. Response time of ~20 seconds.

12

LST

MST

Small

Sized

Telescope

​

Medium

Sized

Telescope

​

Large

Sized

Telescope

​

SST

Among the proposers of GRB observation (2026+) with MAGIC + CTAO/LST:

ET: European 3G GW observatory concept

13

• Delta/ 2L shape
• Length: 10 km (!)
• Underground
• Cryogenic, Increase laser power
• Branchesi & Maggiore 23

On science cases of ET

Sardinian site supported by Italy

3G effort worldwide: Cosmic Explorer (CE)

14

• 2L design; 40 km
• Two sites:

USA

Australia

ET sensitivity:

Branchesi, Maggiore et al 2023

15

• Three different populations
• Flat BNS mass ~1.0-2.5 M_O
• ET-D (Sardinia)/

CE (US)/ CE(Australia)

• Lower freq. down to 2 Hz

-Detection of BNS during inspiral?

-Sky-localization?

-Pre-alert time?

16

Dupletsa et al 2023, Santoliquido et al 2021, Banerjee et al 2023

• ET, CE, CTA synergy to help discovering prompt emission of GRBs in VHE gamma-rays
• 20 VHE counterparts to be detected using ~5% of the CTA time.

Early warning

CBC:

BNS/ NSBH

LVK

Trigger

Confirmed EM counterpart

by X-ray optical telescope

Initiate GMRT observations

Follow-up of gravitational wave events by ground based facilities

Radio (GMRT, India):

TeV gamma-rays (MAGIC+CTAO-LST)

Radio

X-rays

GW 261225/ GRB 261225A

GW experts!

Credit: Ronchini

Radio

Optical

UV

X-rays

MeV

GeV/ TeV

𝜸-rays

GW 261225/ GRB 261225A

Multi-messenger

Astronomy

Exceptional GRBs

Population of GRBs

Exceptional

GW events

Population of

Binary mergers

Unknown Transients

Thesis works

Discoveries

GRB 211211A, GRB 221009A [1, 2],

GRB 250207BDE, GRB 230812B, GRB 210619B, GRB 250702F

A. Ierardi,

P. Tiwari,

S. Macera

A. Ierardi: Mergers

P. Tiwari, S. Macera: Collapsars

! Talk of/ to Samuele !

A. Chopra:

Fast X-ray transients

- Novel correlation of merger driven GRBs

- Typical microphysical parameters for collapsars

P. Tiwari

- Pre-merger alert for GWs for O5

- Typical microphysical parameters for merger driven GRBs

- Origin of FXTs: merger driven?

- Search for Multi-band emission!

Offline search for GW emission from GRBs

Course: GC9 - Foundations of GW and MM data analysis

By F. Santoliquido & B. Banerjee

​

• Gravitational-wave data analysis fundamentals: detector response, data formats, noise properties, and matched filtering for compact-binary signals.
• Bayesian parameter estimation: likelihoods, priors, samplers, posterior inference, and Fisher-matrix forecasts for current and next-generation detectors.
• Deep-learning–based methods for fast parameter estimation and real-time analysis pipelines.
• Multi-messenger observation strategies: coordinating GW triggers with wide-field and pointed gamma-ray and X-ray facilities for prompt and afterglow emission.
• GRB science with GeV–TeV telescopes: jet structure and radiation mechanisms using high-energy gamma rays in a multi-messenger context.
• BNS early-warning and follow-up: low-latency pipelines, sky-localization evolution before merger, and tilling strategies for telescopes.

There are 10³ ways to have fun in L’Aquila!!

​

I know >half of them.