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

Abstract

Aims.Atransientastrophysicaleventobservedinbothgravitationalwave(GW)andelectromagnetic(EM)channelswouldyieldrichscientificrewards.AfirstprograminitiatingEMfollow-upstopossibletransientGWeventshasbeendevelopedandexercisedbytheLIGOandVirgocommunityinassociationwithseveralpartners.Inthispaper,wedescribeandevaluatethemethodsusedtopromptlyidentifyandlocalizeGWeventcandidatesandtorequestimagesoftargetedskylocations.

Methods.Duringtwoobservingperiods(Dec.17,2009toJan.8,2010andSep.2toOct.20,2010),alow-latencyanalysispipelinewasusedtoidentifyGWeventcandidatesandtoreconstructmapsofpossibleskylocations.AcatalogofnearbygalaxiesandMilkyWayglobularclusterswasusedtoselectthemostpromisingskypositionstobeimaged,andthisdirectionalinformationwasdeliveredtoEMobservatorieswithtimelagsofaboutthirtyminutes.AMonteCarlosimulationhasbeenusedtoevaluatethelow-latencyGWpipeline’sabilitytoreconstructsourcepositionscorrectly.

Results.Forsignalsnearthedetectionthreshold,ourlow-latencyalgorithmsoftenlocalizedsimulatedGWburstsignalstotensofsquaredegrees,whileneutronstar/neutronstarinspiralsandneutronstar/blackholeinspiralswerelocalizedtoafewhundredsquaredegrees.Localizationprecisionimprovesformoderatelystrongersignals.Thecorrectskylocationofsignalswellabovethresholdandoriginatingfromnearbygalaxiesmaybeobservedwith~50%orbetterprobabilitywithafewpointingsofwide-fieldtelescopes.