LIGO/Virgo Public Alerts User Guide

GW170817/GRB170817A discovery images

Welcome to the LIGO/Virgo 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.


Some technical details of LIGO/Virgo public alerts may change before the start of Observing Run 3 (O3) in 2019. In particular, details of the alert format and the GraceDb public portal may evolve. Please check this document regularly for announcements and updates.

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

Advanced LIGO and Advanced Virgo are preparing for their third observing run (O3) in early 2019. For the first time, LIGO/Virgo alerts will be public. Alerts will be distributed through NASA’s Gamma-ray Coordinates Network (GCN). There are two types of alerts: human-readable GCN Circulars and machine-readable GCN 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 GCN Notices and decoding GW sky maps.