R. Stone for the LSC Center for Gravitational Wave Astronomy Department of Physics and Astronomy
Interactions between gravitational waves and photon astronomy (periodic signals)
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Transcript of Interactions between gravitational waves and photon astronomy (periodic signals)
October 20, 2007 LSC-VIRGO / NS meeting 1
Interactions between gravitational waves and photon astronomy
(periodic signals)
Ben Owen
October 20, 2007 LSC-VIRGO / NS meeting 2
Intro
• We can look for things better if we know more about them from photon astronomy (we think of 4 NS populations)
• Photon astronomy sets indirect upper limits on GW - milestones for sensitivities of our searches
• GW emission mechanisms influence where we look
• Our interpretation of our results depends on emission mechanisms and previous indirect upper limits
• Some review in Abbott et al gr-qc/0605028
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GW emission mechanisms
• Non-accreting stars (indirect limits beatable now!)– Free precession (looks pretty weak, I’ll skip)
– Elastically supported “mountains” - internal too
– Magnetically supported mountains (Melatos talk)
• Accreting stars (indirect limits beatable with advLIGO…?)– Accretion provides natural mountain building mechanism
– R-mode oscillations build themselves (CFS instability)
– More likely to radiate at indirect limits
• All mechanisms: how high is max & how to drive it there?– Put strength in terms of ellipticity ~ quadrupole, propto h
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Elastic mountains• How big can they be? (Owen PRL 2005)
– Depends on structure, shear modulus (increases with density)
• Standard neutron star – Bildsten ApJL 1998, Ushomirsky et al MNRAS 2000– Thin crust, < 1/2 nuclear density: < few10-7
• Mixed phase star (quark/baryon or meson/baryon hybrid)– Glendenning PRD 1992 … Phys Rept 2001– Solid core up to 1/2 star, several nuclear density: < 10-5
• Quark star (ad hoc model or color superconductor)– Xu ApJL 2003 …, Mannarelli et al hep-ph/0702021– Whole star solid, high density: < few10-4
• Also Lin PRD 2007, Haskell et al arXiv:0708.2984
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Elastic mountains in accreting stars
• How to build high mountains?
• Non-uniform accretion flow hot & cold spots on crust
• Hot spot at fixed density faster electron capture layer of denser nuclei moves upward (non-barotropic EOS)
• If GW balance accretion, is determined by x-ray flux
• Best (Sco X-1) is few10-7, same as predicted max for normal neutron star crust
Bildsten ApJL 1998, Ushomirsky et al MNRAS 2000
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R-modes in accreting stars
• Complicated phenomenology (Stergioulas Living Review)
• 2-stream instability (CFS)
• Viscosity stabilizes modes
• Accretion keeps star balanced at critical frequency … if strange particles are in core
• Max perturbation v/v ~ 10-5 from coupling to other modes
• GW frequency = 4/3 spin freq. minus few % (depends on EOS)
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Four types of neutron stars
• Known pulsars (e.g. Crab)– Position & frequency evolution known (including derivatives,
timing noise, glitches, orbit) Computationally inexpensive
• Unseen neutron stars (e.g. ???)– Nothing known, search over position, frequency & its derivatives
Could use infinite computing power, must do sub-optimally
• Accreting neutron stars (e.g. Sco X-1)– Position known, search over orbit & frequency (+ random walk)– Emission mechanisms different indirect limits
• Non-pulsing neutron stars (“directed searches” e.g. Cas A)– Position known, search over frequency & derivatives
(P>50ms is off our radar)
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Indirect upper limits
• Assume quadrupole GW emission • Use predicted M, R, I (could be off by 2)• Assume energy conservation & all df/dt from GW• Known pulsars - “spin-down limit”
– Best is Crab at 1.410-24
• Non-pulsing NS - substitute age = f/(-4df/dt)
– Best is Cas A at 1.210-24
October 20, 2007 LSC-VIRGO / NS meeting 9
Indirect upper limits• Accreting stars - energy conservation violated
– Assume accretion spin-up = GW spin-down (Wagoner ApJL 1984)
– Infer accretion rate from x-ray flux
– Best is Sco X-1 at 210-26
• Unknown neutron stars - ???– Assume simple population model
– Plug in supernova rate in galaxy
– Most optimistic estimate is 410-24 (Abbott et al gr-qc/0605028)
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Known pulsars
• What we’ve published:– Limits on 1 pulsar in S1: Abbott et al PRD 2004
– Limits on 28 pulsars in S2: Abbott et al PRD 2005
– Limits on 78 pulsars in S3 & S4: Abbott et al PRD 2007
– Note Kramer & Lyne in “et al”: timing data was crucial!
– Best limit was 310-25 for PSR J1603-7202
• When it gets interesting:– Last year (S5) for the Crab! (Pitkin talk)
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Known pulsars
Crab, IL = 710-4
J0537-6910, IL = 910-5
J1952+3252, IL = 110-4
95% confidence thresholdby end of S5
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Known pulsars
• What we’ve published:– Limits on 1 pulsar in S1: Abbott et al PRD 2004– Limits on 28 pulsars in S2: Abbott et al PRD 2005– Limits on 78 pulsars in S3 & S4: Abbott et al PRD 2007– Note Kramer & Lyne in “et al”: timing data was crucial!– Best limit was 310-25 for PSR J1603-7202
• When it’s interesting:– Last year (S5) for the Crab! (Pitkin talk)
• Where we’re going:– Now 97 of 160+ pulsars in our band … but want more! Timing!– Further down the road: SKA would provide us with many more
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Unseen neutron stars
• What we’ve published:– S2 10 hours coherent search (Abbott et al gr-qc/0605028)
– S2 few weeks semi-coherent search (Abbott et al 2005)
– S4 few weeks semi-coherent searches (Abbott et al arXiv:0708.3818)
– Best strain upper limit is 210-24 (sky & polarization combo)
• When it’s interesting:– Already comparable to supernova limit, though that’s fuzzy
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Unseen neutron stars
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Unseen neutron stars
• What we’ve published:– S2 10 hours coherent search (Abbott et al gr-qc/0605028)
– S2 few weeks semi-coherent search (Abbott et al 2005)
– S4 few weeks semi-coherent searches (Abbott et al arXiv:0708.3818)
– Best strain upper limit is 210-24 (sky & polarization combo)
• When it’s interesting:– Already comparable to supernova limit, though that’s fuzzy
• Where we’re going:– S4 & S5 longer datasets (longest coherent integration 25 hours)
– Einstein@Home now on S5 - like SETI@Home but LIGO data, download from http://einstein.phys.uwm.edu
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Directed searches
• What we’re doing:– Cas A (youngest known neutron star?) ~10 days S5
– Galactic center (innermost parsec, good place for unknowns)
• When it’s interesting:– Cas A and any ~100yr old star in center have hIL ~ 110-24
– Doable with present sensitivity!
– Anything detectable now would require solid quark matter
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Directed searches
IL = 10-5
IL = 10-4
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Directed searches
• What we’re doing:– Cas A (youngest known neutron star?) ~10 days S5
– Galactic center (innermost parsec, good place for unknowns)
• When it’s interesting:– Cas A and any ~100yr old star in center have hIL ~ 110-24
– Doable with present sensitivity!
– Anything detectable now would require solid quark matter
• How photon astronomers can help:– Narrow positions on suspected neutron stars (e.g. HESSChandra):
arcminute is OK, arcsecond is better
– Find more young isolated neutron stars, small PWNe and SNRs
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Accreting neutron stars in LMXBs
• What we’ve published (Sco X-1):– S2 6 hours coherent integration (Abbott et al gr-qc/0605028)
– S4 20 days incoherent “radiometer” (Abbott et al astro-ph/0703234)
– Best strain upper limit is 310-24 at 200Hz
• When it’s interesting:– 100 lower than that (Watts talk)
– What kills our sensitivity? Not knowing frequency (orbit too)
• What we’re doing:– Trying to come up with better methods (Krishnan talk)
– Other sources? (Chakrabarty talk, Galloway talk)
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Observational interactions
• Timing data for known pulsars– Jodrell Bank, several others have agreed to more timing– RXTE: J0537-6910 (Marshall et al)
• Timing data for LMXBs– Keeping RXTE alive would be a good thing…– Make friends in India: AstroSat?
• New discoveries (& proposed discoveries)– When you hunt new PSR/CCO/etc, think of indirect GW limits
• Old discoveries– Several NS positions poorly known (ROSAT/XMM), firming up
with Chandra or Hubble would help our searches
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Theory(-ish) interactions
• Interpretation of upper limits– Beating indirect limits on h is more exciting
– How fuzzy are indirect limits? Distances, braking indices…
– Can’t rule out equations of state (stars could just be flat) unless we know mountain building, so what builds mountains?
• Interpretation of detections (let’s hope!)– Frequency confirms emission mechanism (LMXBs)
– R-mode signal means strange particles in core
– High ellipticity means funny equation of state
– Somewhat high means EOS or high internal B field: what max?
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Wrap
• Starting to get interesting sooner than we thought
• More interesting faster w/help from photon astronomy
• Lots of theory stuff to think about too, even if we don’t see anything until advanced LIGO
• Download Einstein@Home!