Implementation and testing of the first prompt search for gravitational wave transients with electromagnetic counterparts

TL;DR

This paper describes the development and evaluation of a low-latency search pipeline for gravitational wave transients with electromagnetic counterparts, enabling rapid localization and follow-up observations during two observing periods.

Contribution

It introduces a prompt search and localization method for GW transients, integrating galaxy catalogs for targeted EM follow-ups, and evaluates its effectiveness through simulations.

Findings

Localized GW signals to tens to hundreds of square degrees.

Localization accuracy improves with signal strength.

Potential for ~50% success in identifying correct sky locations for nearby sources.

Abstract

Aims. A transient astrophysical event observed in both gravitational wave (GW) and electromagnetic (EM) channels would yield rich scientific rewards. A first program initiating EM follow-ups to possible transient GW events has been developed and exercised by the LIGO and Virgo community in association with several partners. In this paper, we describe and evaluate the methods used to promptly identify and localize GW event candidates and to request images of targeted sky locations. Methods. During two observing periods (Dec 17 2009 to Jan 8 2010 and Sep 2 to Oct 20 2010), a low-latency analysis pipeline was used to identify GW event candidates and to reconstruct maps of possible sky locations. A catalog of nearby galaxies and Milky Way globular clusters was used to select the most promising sky positions to be imaged, and this directional information was delivered to EM observatories with time lags of about thirty minutes. A Monte Carlo simulation has been used to evaluate the low-latency GW pipeline's ability to reconstruct source positions correctly. Results. For signals near the detection threshold, our low-latency algorithms often localized simulated GW burst signals to tens of square degrees, while neutron star/neutron star inspirals and neutron star/black hole inspirals were localized to a few hundred square degrees. Localization precision improves for moderately stronger signals. The correct sky location of signals well above threshold and originating from nearby galaxies may be observed with ~50% or better probability with a few pointings of wide-field telescopes.