Gravitational-wave (GW) detectors in the nexus of multi-messenger astrophysics

1. Gravitational-wave (GW) detectors in the nexus of multi-messenger astrophysics Isabel Leonor (University of Oregon) For the LIGO Scientific Collaboration and the Virgo Collaboration LIGO-G0900682

2. Overview: LIGO-Virgo is fully engaged inmulti-messenger astrophysics optical gamma rays, x-rays neutrinos radio TeV Particle Astrophysics, LIGO-G0900682

3. The GRB sample for the LIGO-VirgoS5/VSR1 run GRB triggers were mostly from Swift; some were from IPN3, INTEGRAL, HETE-2 • 212 GRB triggers from Nov. 4, 2005 to Oct. 1, 2007 • ~70%with double-IFO coincidence LIGO data • ~45%with triple-IFO coincidence LIGO data • ~15%short-duration GRBs • ~25% with redshift • during S6/VSR2 run, GRB triggers will be mostly fromFermi+Swift factor of ~3 increase in trigger rate LIGO Hanford average antenna factor Virgo average antenna factor TeV Particle Astrophysics, LIGO-G0900682

4. Search for gravitational-wave burst (GWB)counterparts to GRBs (S5/VSR1 run) • used to search for GW counterpart to both long and short GRBs • burst search is model-independent • targets GW signals less than ~few seconds • fully coherent search which cross-correlates data streams from different interferometers • set 90% upper limits on strain for each GRB • assuming energy emitted in GW results for 137 GRBs (paper due soon) for Advanced LIGO-Virgo D ~ 150 Mpc TeV Particle Astrophysics, LIGO-G0900682

5. Search for GW inspiral signals from GRBs • used to search for GW counterpart to short GRBs • there is evidence that short GRBs are nearer • search makes use of inspiral templates • target GW inspiral signals from coalescing masses in the range 1 M < m1 < 3 M, 1 M < m2 < 40 M • during S5 run, inspiral search range for NS merger event was ~15 Mpc (SNR=8) • for S5 run, 21 short GRBs have been analyzed; no candidate events found • set lower limit on distance for each GRB (paper due out soon) NS-NS merger simulation Price and Rosswog TeV Particle Astrophysics, LIGO-G0900682

6. GRB 070201: In M31 or beyond?GRB or soft gamma repeater (SGR)? (arXiv:0712.1502) • short GRB whose position error box overlapped with spiral arms of Andromeda galaxy (M31, ~770 kpc) • occurred during LIGO S5 run; two Hanford interferometers were in science mode • inspiral search analysis excludes binary merger event at M31 with >99% confidence; larger distances also excluded with high confidence • burst search analysis gives upper limits on GW energy released; these limits do not exclude a model of a soft gamma repeater in M31(ApJ, 2008, 681, 1419) TeV Particle Astrophysics, LIGO-G0900682

7. Search for GW bursts coincident with soft gamma repeater (SGR) bursts Robert Mallozzi (UAH, MSFC) • SGRs thought to be highly magnetized neutron stars (~1E+15 G) • most observed SGRs are Galactic • SGR bursts from crustal deformations and catastrophic cracking may be accompanied by GW burst emission • search for excess power from GW burst relies on SGR lightcurves from Interplanetary Network (IPN3), including Swift, Konus-Wind, etc. • 191 bursts from SGR 1806-20 and SGR 1900+14 have been analyzed for coincident GW emission using LIGO • some of the upper limits set on GW energy emission already explore some SGR models 90% UL on energy of GW emission coincident with 215 SGR bursts (PRL, 2008, 101, 211102)

8. Search for GW burst emission from anSGR storm (SGR 1900+14) 30 seconds SGR 1900+14 lightcurve (Mar 29, 2006) from Swift-BAT telescope • assume GW signal accompanies each storm episode • “stacking” power from different storm episodes leads to increased GW search sensitivity requires precise timing from SGR lightcurve for start time of each storm episode • resulting upper limits on GW energy emission ~order of magnitude lower than non-stacked analysis(arXiv:0905.0005) TeV Particle Astrophysics, LIGO-G0900682

9. Search for periodic GW signals from known pulsars • target signal: monochromatic signals emitted by pulsars • most likely mechanism for production of detectable GW is small distortions of the NS shape away from axisymmetry • search at GW frequency twice the pulsar rotation frequency • search method makes use of a signal template for each pulsar requires updated ephemeris data to model phase evolution of pulsar signal requires collaboration with radio pulsar astronomers • S5 best limit: h0=2.3E-26 at the sweet spot (paper due soon) • best ellipticity limit of 7E-8 Jodrell Bank Parkes Telescope Green Bank 116 known pulsars 95% upper limits (preliminary)

10. Crab pulsar: beating the spin-down limit Credits: X-ray: NASA/CXC/ASU/ J. Hester et al.; Optical: NASA/HST/ASU/ J. Hester et al. • spin-down limit assumes all the pulsars rotational energy loss is radiated by gravitational wave • we know some energy is emitted electromagnetically and is powering the expansion of the Crab nebula • this is poorly constrained and allows room for gravitational wave emission • search method depends on data from Jodrell Bank Crab Pulsar monthly ephemeris to track the phase • using first nine months of LIGO S5 data, obtain 95% upper limit on strain amplitude of h0=2.7E-25 lower than classical spin-down limit by a factor of ~5 (ApJ, 2008, 683, L45) • using entire S5 data gives UL which beats spin-down limit by ~7 Jodrell Bank

11. Swift target of opportunity (ToO) • during S6/VSR2, possible GW candidates from all-sky burst and inspiral searches will be verified by requesting electromagnetic follow-up observations • X-ray follow-up will be requested from Swift • LIGO-Virgo error box will be ~few degrees • verification of astrophysical object by an EM counterpart will further probe nature of object • anticipates era of regular GW detections using more sensitive detectors, i.e. Advanced LIGO, Advanced Virgo TeV Particle Astrophysics, LIGO-G0900682

12. Swift target of opportunity (ToO) • during S6/VSR2, possible GW candidates from all-sky burst and inspiral searches will be verified by requesting electromagnetic follow-up observations • X-ray follow-up will be requested from Swift • LIGO-Virgo error box will be ~few degrees • verification of astrophysical object by an EM counterpart will further probe nature of object • anticipates era of regular GW detections using more sensitive detectors, i.e. Advanced LIGO, Advanced Virgo TeV Particle Astrophysics, LIGO-G0900682

13. LOOC UP Locating and Observing Optical Counterparts to Unmodeled Pulses in gravitational waves • for S6/VSR2 run, position information of GW triggers from all-sky burst search will be sent to available optical telescopes via automated interface • imaging/follow-up will be requested from telescopes • expect initial latency of ~30-60 minutes from GW trigger to imaging • LOOC UP currently pursuing MOU’s with telescopes (SkyMapper, ROTSE, TAROT, etc.) TeV Particle Astrophysics, LIGO-G0900682

14. Gravitational waves and neutrinos (nascent collaborations) Borexino LVD Super-K IceCube ANTARES TeV Particle Astrophysics, LIGO-G0900682

15. Supernova early warning system (SNEWS)http://snews.bnl.gov • alert system which would send out notification of high-confidence SN to astronomical community a few minutes after detection of neutrino burst by multiple detectors • LIGO-Virgo is signed up to get these alerts in the control rooms • low-latency search for a GW signal coincident with a SNEWS trigger is planned for the LIGO-Virgo S6/VSR2 run • there is a proposed joint GW-neutrino search which will complement the existing infrastructure and procedures which are in place in the event of a SNEWS alert TeV Particle Astrophysics, LIGO-G0900682

16. Estimates of Galactic and nearby core-collapse supernova rate Ando, S. et al. 2005, PRL, 95, 171101 • estimated Galactic rate is a few (~3) per century • estimated rate in Local Group (out to ~1 Mpc) ~twice the Galactic rate • ~1 per year out to the Virgo cluster • observations indicate that the true nearby SN core-collapse rates could be higher than these estimates (e.g. ~3 times higher, using observed SN in 2002-2005) • electromagnetically dark or obscured SN would also bring uncertainties to these rates TeV Particle Astrophysics, LIGO-G0900682

17. LIGO sensitivity and expected improvement with joint neutrino search 153 Hz • in contrast to neutrino signal, energy emitted as GW radiation is expected to be small • currently, there are large uncertainties in models of core-collapse SN, e.g. simulations have difficulty making a SN explode • like neutrino signal, GW signal would probe the innermost region of SN core • requiring coincidence of GW and neutrino signals to within a short time window of ~few seconds would allow lower detection thresholds Andromeda LMC Energy into GW (solar masses) Distance (kpc) Models for GW emission (from Ott, C. 2009, CQG, 26, 063001) A: PNS pulsations B: rotational instability C: rotating collapse and bounce D: convection and SASI  improvement in sensitivity TeV Particle Astrophysics, LIGO-G0900682

18. Joint search could benefit neutrino search as well Detection probability LMC Andromeda • criterion for neutrino search can be relaxed • example: for Super-K distant SN search, criterion is at least 2 neutrino events per 20 seconds and high energy threshold of 17 MeV • if coincidence with GW signal is used, then criterion can be relaxed to a single neutrino event; odds will increase that distant core-collapse will satisfy this criterion • energy threshold could also be lowered Probability of satisfying criterion Distance to supernova (kpc) standard criterion relaxed criterion TeV Particle Astrophysics, LIGO-G0900682

19. Gravitational waves and high-energy neutrinos ANTARES (Mediterranean Sea) • currently a collaborative effort between LIGO, Virgo, IceCube, ANTARES • joint GW and high-energy neutrino search will lower background rate • both GW and high-energy neutrino signals travel long distances without absorption • possible sources: long and short GRBs, low-luminosity GRBs, failed GRBs, soft gamma repeaters • overlapping GW and neutrino data is available from past runs (S5/VSR1) and will be available from future runs (S6/VSR2 and beyond) IceCube (South Pole) TeV Particle Astrophysics, LIGO-G0900682

20. Other current or future multi-messenger activities • analysis of Swift data to extract sub-threshold events (possible GRBs) which can increase GRB sample which serve as triggers to GW analysis • analysis is currently ongoing (E. Harstad, University of Oregon) • search for GW bursts coincident with pulsar glitches • search for GW signal associated with RXTE observations of Sco X-1 • radio-triggered searches for GW bursts • … TeV Particle Astrophysics, LIGO-G0900682

21. Summary LIGO and Virgo are fully engaged in multi-messenger astrophysics These multi-messenger analyses continue to be pursued during the current S6/VSR2 run These activities and the nascent collaborations serve as a strong foundation for analyses of future, more sensitive data as an era of regular GW detections is anticipated with Advanced LIGO-Virgo TeV Particle Astrophysics, LIGO-G0900682