The first six months of the Advanced LIGO's and Advanced Virgo's third observing run with GRANDMA

TL;DR

GRANDMA is a global network of 21 telescopes designed to rapidly follow up on gravitational-wave events and other transients, improving detection and characterization of electromagnetic counterparts during LIGO-Virgo's third observing run.

Contribution

This paper introduces the GRANDMA network, its infrastructure, tools, and methods, and demonstrates its effectiveness in follow-up observations during LIGO-Virgo's third run.

Findings

Successful follow-up of LIGO/Virgo S190425z event.

Constraints on kilonova properties from observed data.

Enhanced coordination reduces delay in electromagnetic counterpart detection.

Abstract

We present the Global Rapid Advanced Network Devoted to the Multi-messenger Addicts (GRANDMA). The network consists of 21 telescopes with both photometric and spectroscopic facilities. They are connected together thanks to a dedicated infrastructure. The network aims at coordinating the observations of large sky position estimates of transient events to enhance their follow-up and reduce the delay between the initial detection and the optical confirmation. The GRANDMA program mainly focuses on follow-up of gravitational-wave alerts to find and characterise the electromagnetic counterpart during the third observational campaign of the Advanced LIGO and Advanced Virgo detectors. But it allows for any follow-up of transient alerts involving neutrinos or gamma-ray bursts, even with poor spatial localisation. We present the different facilities, tools, and methods we developed for this network, and show its efficiency using observations of LIGO/Virgo S190425z, a binary neutron star merger candidate. We furthermore report on all GRANDMA follow-up observations performed during the first six months of the LIGO-Virgo observational campaign, and we derive constraints on the kilonova properties assuming that the events' locations were imaged by our telescopes.