1. Follow-up of LIGO-Virgo observations of gravitational waves Roy Williams (Caltech) Peter Shawhan (U. of Maryland / JSI) for the LIGO Scientific Collaboration and Virgo Collaboration Hot-Wiring the Transient Universe November 14, 2013 LIGO-G1301197

2. ))) Advanced Gravitational Wave Detectors 2 Factor 10 in strain means factor 1000 in volume. Long-planned upgrades of initial GW detectors: Advanced LIGO (shown) and Advanced Virgo

3. ))) … Now Being Installed and Tested ! 3

4. ))) 4 Advanced Detector Network – Under Construction GEO-HF Advanced VIRGO Advanced LIGO 4 km 600 m 3 km 4 km (pending)

5. ))) Searches for GW Transient Sources GW data streams are analyzed jointly Initially LIGO Hanford+Livingston and Virgo; later others too Two main types of transient searches: Compact Binary Coalescence (CBC) Known waveform  Matched filtering Templates for a range of component masses (spin affects waveforms too, but not so important for initial detection) Unmodelled GW Burst (< ~1 sec duration) e.g. from stellar core collapse Arbitrary waveform  Excess power Require coherent signals in detectors, using direction-dependent antenna response 5 Credit: AEI, CCT, LSU Credit: Chandra X-ray Observatory

6. Projecting Advanced LIGO Sensitivity Progression 2015-2018 6 2016-17: ~ 6 month run, 80 - 120 Mpc Likely Detection 2016-17: ~ 6 month run, 80 - 120 Mpc Likely Detection 2017-18: ~ 9 month run, 120 - 170 Mpc Multiple Detections 2017-18: ~ 9 month run, 120 - 170 Mpc Multiple Detections 2010: Initial LIGO, 15 Mpc 2015: ~ 3 month run, 40 - 80 Mpc Possible Detection 2015: ~ 3 month run, 40 - 80 Mpc Possible Detection From “Prospects for Localization of Gravitational Wave Transients by the Advanced LIGO and Advanced Virgo Observatories” arXiv:1304.067 0

7. ))) Low-latency GW Event Candidates Multiple analysis pipelines running as data is collected Generate triggers from apparent transients in the data Estimate significance by comparing with background distribution from time-shifted analysis 7 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

8. ))) EM and GW WHY Multimessenger? Brilliant science from optical counterparts of GRBs (1998) Brilliant science from neutrino counterparts of Supernova 1987A EM  GW: Short GRBs and galactic SN Will trigger a search for GW counterpart, short/long latency SWIFT, Fermi, SNEWS GW  EM: Rapid alerts to telescope partners Wide area search for counterpart (cf Singer talk) Could be quite faint and red (cf Nissanke talk) 8

9. ))) What info from GW observatory Time of the GW candidate At Earth, with precision of order ~10 ms (direction-dependent) Significance of the candidate Expressed as an effective false alarm rate (FAR) Sky position probability map HEALPix grid in FITS file Maximum Distance Although the source could be much closer Expect to distribute GW alerts as VOEvents over (initially) private GCN/TAN, VOEventNet and/or Skyalert 9

10. ))) Alert Latency and Notes Typical latency to generate triggers with sky position info: 3 to 6 minutes Additional time needed for validation: not yet known, but maybe ~20 min We might provide multiple skymaps with different assumptions about the source CBC orbit inclination: unconstrained, or face-on GW burst polarization: unconstrained, linear, or elliptical We may send updated information about an event after the initial alert e.g. refined skymap or significance estimate Will send a VOEvent referencing the first one, incrementing the version number in the IVORN 10

11. ))) Position Reconstruction Accuracy vs. Time Face-on BNS 160 Mpc HLV 2019+ ~30 % contained in 20 deg 2 Face-on BNS 160 Mpc HILV 2022+ ~50 % contained in 20 deg 2 Face-on BNS 80 Mpc HLV 2016-17 ~8 % contained in 20 deg 2 Face-on BNS 80 Mpc HLV 2017-18 ~10 % contained in 20 deg 2 11

12. ))) Simulated skymaps Posterior probability skymaps are obtained from coherent analysis Fast coherent position reconst. (~min) Full parameter estimation can be done, but currently is slow (~days), effort underway to reduce to ~hour) 12 On gamma sky (Fermi) Examples of BAYESTAR skymaps from simulated signals L. Price, L. Singer, et al On Mellinger sky

13. ))) Simulated Skymaps Error region geometry can be non-trivial Banana shape and/or Disconnected islands – especially for narrowband GW burst candidates No single "sky position" quoted in alerts to observers 13

14. ))) LIGO-Virgo Approach to Partnerships Basic Concept: Share triggers with observers who sign MOUs Confident detection of first few GW signals will require time and care— need to avoid misinformation/rumors/media circus Partners who sign standard MOUs will receive GW triggers promptly, exchange results, decide their own observations, analyze own data Any apparent counterpart, may not be published or presented prior to the announcement by LIGO/VIRGO After 4 GW events have been published, further high-confidence events will be released promptly to the public Have sought advice and input from the astronomical community Solicited “letters of interest” – received about 60 Held meetings in Amsterdam (late August) and Chicago (mid September) Very encouraging show of interest! Feedback and suggestions from meetings have shaped some of the plans for the program 14

15. ))) Summary Gravitational wave detectors operate as a global network Data combined and analyzed coherently Japan and/or India critical for good localization Advanced LIGO and Virgo upgrades are well underway First science run is only about 2 years away Sensitivity and position reconstruction accuracy will improve over time EM follow-ups are exciting Whether for the first few GW detections, or later on Now engaging follow-up observers. Want to get involved? Write lsc-spokesperson@ligo.org (Gabriela González), and/or virgo-spokesperson@ego-gw.it (Jean-Yves Vinet).

16. ))) Extra Slides… 16

17. ))) Observing Partners During 2009–2010 17 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

18. ))) Observing Partners During 2009–2010 18 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

19. ))) First Implementation: 2009–2010 Analyzed 3-detector data during 10 weeks of LIGO-Virgo running Low-latency CBC and Burst searches Sent alerts to ten follow-up partners Selected (RA,Dec) points, targeting nearby galaxies in GW error region Various communication protocols and feedback methods General description: A&A 539, A124 CBC low-latency analysis: A&A 541, A155 Eight event candidates were followed up by at least one telescope No stand-out candidates, unfortunately Swift (XRT/UVOT) image analysis results: Evans et al., ApJS 203, 28 Ground-based telescope analysis results: Aasi et al., arXiv:1304.0670 Lessons learned: standardize, give observers more freedom 19 +VLA (later)

20. ))) Possible VOEvent content for a GW alert 20 CBC GW burst IVORN ivo://gwnet/[GraceDBID]-[version] Who LIGO Scientific Collaboration and Virgo Collaboration WhereWhen Estimated geocentric arrival time What GraceDB ID Alert version number Link to FITS skymap Link to GraceDB event page Chirp massPeak frequency Symmetric mass ratioBurst duration Approx. maximum distanceEnergy fluence at Earth Why All-sky all-time search or triggered search (by a GRB, e.g.) How Name of the event trigger generator which found this event (e.g. "gstlal", "MBTA", "cWB", "cWB-linear") List of the LIGO-Virgo detectors contributing to this event preliminary