LIGO/Virgo/KAGRA Public Alerts User Guide

GW170817/GRB170817A discovery images

Welcome to the LIGO/Virgo/KAGRA Public Alerts User Guide! This document is intended for both professional astronomers and science enthusiasts who are interested in receiving alerts and real-time data products related to gravitational-wave (GW) events.

Four sites (LHO, LLO, Virgo, KAGRA) together form a global network of ground-based GW detectors. The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration jointly analyze the data in real time to detect and localize transients from compact binary mergers and other sources. When a signal candidate is found, an alert is sent to astronomers in order to search for counterparts (electromagnetic waves or neutrinos).

LIGO/Virgo/KAGRA alerts are public. Alerts are distributed through NASA’s General Coordinates Network (GCN, and Scalable Cyberinfrastructure to support Multi-Messenger Astrophysics (SCiMMA, There are two types of alerts: human-readable GCN Circulars and machine-readable Notices. This document provides a brief overview of the procedures for vetting and sending GW alerts, describes their contents and format, and includes instructions and sample code for receiving Notices and decoding GW sky maps.