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

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: Einstein@Home 14th GWDAW, Jan. 2010

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

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

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

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

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

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 7×10-4 Improved results using nebula inclination One search following radio timing (or should have) (superseded by result in next 2 slides) One search over range of frequencies, 1st derivatives GW & photon emitters could be separate Max.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

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

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×, J0537-6910 6×, 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

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

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

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

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

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

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

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 Einstein@Home: 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