1. Searches for continuous gravitational waves in the advanced detector era
Ra Inta (Texas Tech University)
for the LIGO Scientific Collaboration and the Virgo Collaboration
LIGO Document G v4

2. No Continuous gravitational Waves (CW) detected… yet!
Most searches begin after an observing run has ended
Still analysing LIGO O1 data

3. CW Sources LIGO/Virgo band: O(10) Hz – O(1) kHz
Rotating neutron stars with some non-axisymmetry
Axions?

4. Animation: Joeri van Leeuwen

5. Triaxial model

6. Deviation from axisymmetry: ellipticity
Determines maximum height of ‘hills’ supported within NS crust ( O(few) cm )

7. Expected amplitudes

8. Expected amplitudes Abbott, B.P. et al., PRL 116:061102 (2016)
Caltech/MIT/LIGO Lab
Abbott, B.P. et al., PRL 116: (2016)

9. Expected amplitudes

10. Fluid modes
r-mode instability
B. Owen/C. Hanna

11. Precession
(plus side-bands)
M. Kramer

12. Neutron star population

13. Neutron star population
Where are the other ~108 neutron stars?

14. aLIGO sensitivity ~17% of (known) pulsars ~23% of (known) pulsars
B.P. Abbott et al., PRL 116: (2016)

15. Computational bound
Averaging means most CW searches are computationally limited e.g.: typical, modest, search takes ~400,000 CPU hrs on Albert Einstein Institute’s Atlas supercomputer Bounds often explicitly used to determine a figure of merit for CW searches

16. What if we make a detection?
Follow-up with multiple search pipelines
Compare GW phase to EM pulse timing
Potential for EM follow-up
Potential confirmation of many neutron star properties
Test General Relativity
Constrain neutron star equation of state

17. D. Page

18. Adapted from Horowitz, C.J. and Kadau, K., PRL 102:191102 (2009)

19. Types of CW searches

20. 1) Targeted searches What we know: α, δ, f0, df/dt
Searches can be narrow-band around parameters
Three pipelines
NASA/ESA/J. Hester/A Loll

21. 1) Targeted searches Crab Vela Meaningful limits on Vela and Crab
Good prospects for aLIGO!
Aasi, J et al., ApJ. 785:119 (2014)

22. 1) Targeted searches Narrow-band around parameters of Crab and Vela
Robust w.r.t to model assumptions
Looked at five partial harmonics per target
Meaningful upper limits set on both: 0.50 and 0.97 expected (spin-down) h0 respectively
Aasi, J. et al., PRD 91: (2015)

23. 2) Directed searches What we know: α, δ
Search over: f0, df/dt, d2f/dt2, …
NASA/Chandra/STScI/Spitzer

24. 2) Directed searches Young supernova remnants
Adapted from NASA/JPL-Caltech/ESO/R. Hurt., with permission
Aasi, J. et al. ApJ. 813(1) 39 (2015)

25. 2) Directed searches
Beat age-based upper limit on nine supernova remnants
Constraints on r-mode amplitudes
Many more targets in O1
Aasi, J. et al. ApJ. 813(1) 39 (2015)

26. Sco-X1 Sco-X1 Mock Data Challenge J.T. Whelan’s talk Y. Zhang’s talk
G. Meadors’ poster
Sco-X1 Mock Data Challenge
Aasi, J. et al., PRD 91: (2015)
Messenger, C. et al., PRD 92: (2015)

27. 3) All-sky searches
What we know: -
Search over: α, δ, f0, df/dt, …

28. 3) All-sky searches Low frequency all-sky (frequency Hough) --- Virgo
Virgo VSR2 and VSR4 data
Hierarchical Hough-transform in frequency domain
Best upper limits below 80 Hz
Aasi, J. et al., PRD 93: (2016)

29. 3) All-sky searches PowerFlux (S6)
Most comprehensive coverage of parameter space to date
Uses distribution-free ‘universal statistic’ to reduce impact of non-Gaussian noise
‘Loosely coherent’ follow-up
arXiv:

30. 3) All-sky searches: binaries
TwoSpect
Polynomial
Aasi, J. et al., PRD 90: (2014)

31. 3) All Some-sky searches
Loosely coherent search in Orion's Spur
Deeper search in small patch of sky
Multiple stages of increasing coherence
Identified 70 candidates
Three most significant ruled out by other pipelines
Aasi, J. et al., PRD 93: (2016)

32. Pipeline optimisation and improvements
Directed search optimisations -- J. Ming’s talk
Parameter space improvements -- Wette, K., PRD 92: (2015); Jones, D.I., MNRAS 453:53 (2015); Leaci, P., and Prix, R., PRD 91: (2015)
Searches for time-limited CWs -- Keitel, D., arXiv:
Semi-coherent all-sky improvements -- Goetz, E. and Riles, K., CQG 33: (2016)
Non-GR alternatives -- Isi, M. et al., PRD 91: (2015) -- see M. Isi’s poster
Many more!

33. Summary and the future Many improvements made to search pipelines
Increasingly better upper limits and parameter space coverage
No detection… yet
The future looks bright!

34. How can you get involved?
A. Singh’s talk