Following Up Gravitational Wave Event Candidates Roy Williams (Caltech), Peter Shawhan (U Maryland), for the LIGO Scientific Collaboration and Virgo Collaboration LSST All Hands Meeting 2012 August 14 LIGO-G

))) Sources of Gravitational Waves ► Compact binary coalescence ► Stellar core collapse e.g. neutron stars or black holes ► Neutron stars ► Cosmic strings Periodic from bump Non-periodic from flare ► Early Universe Like CMB The challenge: Expected strain amplitudes at Earth are 10 –21 or less 2 h(t) Bill Saxton, NRAO/AUI/NSF Casey Reed/PSU )))))) ► and others…

))) A Full-Size GW Detector 3 LIGO Hanford Observatory (Washington state, USA)

))) Advanced LIGO will be a Vast Improvement 44 Factor of ~10 better amplitude sensitivity than initial detectors  Factor of ~1000 greater volume of space Best estimate: will detect dozens of mergers per year* *”Rates paper” Image courtesy Beverly Berger and atlasoftheuniverse.com

))) 5 Advanced Detector Network, ~2015 and Later GEO-HF Advanced VIRGO Advanced LIGO 4 km 4 km 600 m 3 km LIGO-India (proposed) KAGRA

))) Global GW Observatory Sky localization by time differences Data courtesy LIGO/LSC ROUGH GUIDE to typical error region areas: 2 detectors: ~1000 square degrees (annulus) 3 detectors: tens/hundreds square degrees 4 detectors: ~10 square degrees Need at least 3 operating detectors to localize signals Coordinate science runs and downtimes when possible

))) Impact of Follow-up Observations Finding an optical/radio/X-ray/neutrino transient will put the GW event candidate in an astronomical context Much more science! May be able to confidently detect a somewhat weaker GW event (spectral) Localize in a host galaxy (or outside!) Compare GW and electromagnetic emissions: strength, time, etc. Allow better parameter estimation from the GW data Need to manage probability of false (unrelated) associations Classification of transients will be essential Should have a handle on the normal population of similar transients 7 In 2009–2010: Program active for 10 weeks of LIGO-Virgo joint observing Nine event candidates were followed up by at least one telescope Including two by Swift (XRT & UVOT) No stand-out candidates, unfortunately [ Evans et al., arXiv: ] Multi-messenger astronomy 7

))) Supernova vs Binary Inspiral Binary Coalescence is an impact  Fainter But bright along jet axis (= short GRB) 8 CC Supernova is a detonation  BRIGHT Can be seen to edge of Universe Metzger and Berger

))) LSST is Essential The range of existing SGRB optical afterglows … indicates that observations with LSST are essential. -- Metzger and Berger 9 On Axis Off Axis observation upper limit Post merger accretion Van Eerten/MacFadyan Isotropic kilonova Metzger and Berger Figs: Metzger and Berger

))) Rapid Alerts for Follow-up Observations Goal: Catch a counterpart that would have been missed (or detected only later) Missed GRB, orphan afterglow from off-axis or “failed” GRB, kilonova, …  Localize accurately, compare GW & EM emissions 10 LIGO Hanford LIGO Livingston GEO 600 Virgo LIGO-India KAGRA GW data Analyze data, identify triggers, infer sky position Estimate background Trigger database Select event candidates Validate Transfer data Send info to observers Swift: NASA E/PO, Sonoma State U., Aurore Simonnet

))) Communication with Follow-up Observers Assemble event candidate information Type of signal, significance, time, sky map, estimated physical params (?) Format as a VOEvent, for instance Send alert to observers Plan to use standard channel(s) like GCN/TAN, VOEventNet May have revised / refined information to distribute later LSC and Virgo committed to releasing public alerts in the long run Early on, work with partners through MOUs until a few GWs are detected Policy: 11

))) Observing Partners During 2009– XRT UVOT APERTURE 2 m 1 m 1.2 m 1.3 m 1 m Mostly (but not all) robotic wide-field optical telescopes Many of them used for following up GRBs, surveying for supernovae and other optical transients LSST, 6.7m

))) Observing Partners During 2009– FIELD OF VIEW XRT UVOT 20×20° 7.3 sq deg 9.4 sq deg 25 sq deg 3.4 sq deg 5.7 sq deg 3.4 sq deg Mostly (but not all) robotic wide-field optical telescopes Many of them used for following up GRBs, surveying for supernovae and other optical transients LSST

))) Event of the “Big Dog” Top 1000 pixels reported total area: 129 sq deg est. containment: ~19% 14 Coherent WaveBurst probability sky map: The “Big Dog” Phase rings 160

))) 15 Galaxy Prior Probably (maybe not*) GW sources stay near their places of birth … Use positions of known galaxies within 50 Mpc White et al., CQG 28, Star formation proxy = blue light luminosity Galaxies not so useful at 200 Mpc – too many. False positives are concentrated on the galaxies * Fong et al

))) Follow-up for Big Dog nearby galaxies TAROT, ROTSE Swift SkyMapper Zadko 16 Images taken within 44 min after event, 2 min after LIGO event, and on subsequent nights … turned out to be blind injection 

Summary Gravitational wave detectors are operated as a global network Data combined and analyzed coherently Advanced LIGO and Virgo upgrades are in progress First science runs planned for 2015–16 Might be years to full sensitiviy and good localization KAGRA and LIGO-India to join too Have begun a program of producing and sending rapid alerts Supports both prompt and delayed follow-up observations Many lessons learned from the 2009–10 science run Now preparing an improved future program with easy MOU Transition to public alerts planned after detection of 4 GW events