1. Continuous gravitational waves: Observations vs. theory
Ben Owen
(Penn State & LIGO-Caltech)
for the LIGO Scientific Collaboration
and the Virgo Collaboration
14th GWDAW, Jan. 2010

2. Continuous GW data analysis
“Permanent” nearly-sinusoidal signals
Slow frequency changes due to Earth’s motion
Slow intrinsic changes
Too much parameter space to coherently search it all: pick targets or go semi-coherent (SEVERAL TALKS, POSTERS)
Image:
14th GWDAW, Jan. 2010

3. Continuous GW sources Now
“Mountains”: static ellipticity ε on rotating “neutron” star = time-dependent quadrupole
Magnetic: field lines have tension, buoyancy
Elastic: crust of neutron-rich matter + core if quarks etc.
Modes of oscillation
Long-lived ones are r-modes
Free precession
Image: K. Hokusai
Image: C. Hanna & B. Owen
Soon
Later
14th GWDAW, Jan. 2010

4. How big could the asymmetry be?
R-modes: complicated (… BONDARESCU ET AL. 2009)
Magnetic: ellipticity ε ~ (10-6−10-5) × (B/1015G)2 (CHANDRA & FERMI 1953 … COLAIUDA ET AL. 2008)
Elastic mountains: max. ε? (OWEN 2005 …)
10-2
Quarks
10-3
10-4
Hybrids No
lower
limit
10-5
NS crust
10-6
14th GWDAW, Jan. 2010

5. What could drive it to maximum?
Accretion
Torque balance / spin rates (… BILDSTEN 1998)
Electron capture
Magnetic bottling
R-modes (ANDERSSON ET AL. 1999)
But in young stars …?
R-modes (OWEN ET AL. 1998)
Post-supernova mess?
(Ushomirsky et al. 2000)
Image: A. Piro
(Melatos & Payne 2005)
14th GWDAW, Jan. 2010

6. Observations Photons tell us where to look, helps data analysis
S4 searches had O(10) variation in h0 amplitude
And set indirect upper limits on GW we need to beat
Known pulsars (e.g. Crab): spin-down limit; also depends on distance, moment of inertia, ~2× uncertainty
Unknowns (all-sky surveys): population stats limit (later)
Accreting stars (pulsing or not, e.g. Sco X-1): x-ray flux limit if torque balance holds; depends on star, magnetosphere
Other directions (e.g. Cas A): age-based limit
Best x-ray indirect limit O(10-26), best others O(10-24)
14th GWDAW, Jan. 2010

7. Crab pulsar Highest spin-down power in galaxy
Pulsar timed daily in radio, now and then in every EM band
Most studied pulsar wind nebula
Image: Chandra/NASA
14th GWDAW, Jan. 2010

8. Crab pulsar LIGO S5 1st 9 months (up to August 2006 glitch)
Beat spin-down limit h0 < 1.4×10-24, ε < 7×10-4
Improved results using nebula inclination
One search following radio timing (or should have)
(superseded by result in next 2 slides)
One search over range of frequencies, 1st derivatives
GW & photon emitters could be separate
Max. glitch amplitudes, relaxation times indicate O(10-4)
95% confidence upper limits h0 < 1.2×10-24, ε < 6×10-4
14th GWDAW, Jan. 2010

9. Known pulsars in LIGO band
14th GWDAW, Jan. 2010

10. Known pulsars in LIGO band
LIGO full S5 run (2 years)
116 pulsars of ~200 known in LIGO band (timing)
LSC + Virgo + 15 radio & x-ray co-authors
Glitches: Crab 1×, J ×, another 1×
Integrate epochs separately; or
Integrate all, GW always following radio timing; or
Integrate all, unknown relative phase jumps at glitches
Crab: h0 < 2×10-25, ε < 1.0×10-4 (spin-down ×1/7)
J0537: h0 < 4×10-26, ε < 1.2×10-4 (spin-down ×1.3)
14th GWDAW, Jan. 2010

11. Vela pulsar current status
GW frequency 22 Hz, where Virgo is more sensitive than LIGO
Radio timing daily
Several months VSR2 data
3 analysis pipelines converging (ASTONE, KROLAK TALKS)
Projected sensitivity comparable to spin-down limit h0 < 3×10-24, ε < 2×10-3
Image: Chandra/NASA
14th GWDAW, Jan. 2010

12. What do the observations mean?
First you have to beat the spin-down limit
And fuzzier indirect limit if braking index is known
Phenomenological spin-down model (PALOMBA 2000) estimates spin-down ×0.4 (Crab) or ×0.2 (Vela), not possible for J0537 due to frequent glitches
Could have seen the Crab if it’s a lumpy quark star
Upper limits do NOT constrain composition or EOS
Do constrain internal B-field (Crab < ~1016G)
Haven’t looked for r-modes yet (frequency etc.)
14th GWDAW, Jan. 2010

13. All-sky survey for unknown objects
LIGO S5 1st 8 months (compute-limited)
Semi-coherent w/30 minutes coherent time
Frequency 50−1100 Hz, |fdot| 0−5×10-9 Hz/s (~10× Crab spin-down)
Polarization-averaged h0 < 1×10-24 in dip
14th GWDAW, Jan. 2010

14. What do the observations mean?
Know supernova rate, spatial distribution (…)
Statistically estimate max. h0 per octave
GW observations mean one or more of
Birth rate < 1/30 years
Typical ε < 10-6
Typical P > 10 ms
(Knispel & Allen 2008)
14th GWDAW, Jan. 2010

15. Central compact object in Cas A
X-ray point source in supernova remnant
Youngest known neutron star: 300 years
No pulsations or other variability found, and not for lack of trying (best studied remnant in galaxy)
Image: Chandra/NASA
14th GWDAW, Jan. 2010

16. Central compact object in Cas A PRELIMINARY RESULTS
LIGO S5 12 days (computationally limited)
Frequencies 100−300 Hz (best noise), 1st and 2nd derivative ranges based on braking indices 2−7
Beat indirect limit, great ε, hope frequency is right
14th GWDAW, Jan. 2010

17. Near-future improvements
More searches like Cas A are interesting, including galactic center (BEHNKE POSTER)
Always glad to get more pulsars, more timing
All-sky surveys
more CPUs, coherence time, sensitivity
Adding binaries (GOETZ, BULTEN POSTERS)
All of these plus accreting stars: improved data analysis methods (OTHER TALKS AND POSTERS)
14th GWDAW, Jan. 2010