Interactions between gravitational waves and photon astronomy (periodic signals)

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Interactions between gravitational waves and
photon astronomy(periodic signals)

• Ben Owen

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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, Ill 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, lt 1/2? nuclear density ? lt few?10-7
• 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 ? lt 10-5
• Quark star (ad hoc model or color superconductor)
• Xu ApJL 2003 , Mannarelli et al hep-ph/0702021
• Whole star solid, high density ? lt few?10-4
• Also Lin PRD 2007, Haskell et al arXiv0708.2984

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Elastic mountains in accreting stars
Bildsten ApJL 1998, Ushomirsky et al MNRAS 2000

• 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 few?10-7, same as predicted max
  for normal neutron star crust

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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
(Pgt50ms is off our radar)

• 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

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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 1.4?10-24
• Non-pulsing NS - substitute age f/(-4df/dt)
• Best is Cas A at 1.2?10-24

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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 2?10-26
• Unknown neutron stars - ???
• Assume simple population model
• Plug in supernova rate in galaxy
• Most optimistic estimate is 4?10-24 (Abbott et al
  gr-qc/0605028)

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Known pulsars

• What weve 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 3?10-25 for PSR J1603-7202
• When it gets interesting
• Last year (S5) for the Crab! (Pitkin talk)

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Known pulsars
Crab, ?IL 7?10-4
J19523252, ?IL 1?10-4
95 confidence threshold by end of S5
J0537-6910, ?IL 9?10-5
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Known pulsars

• What weve 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 3?10-25 for PSR J1603-7202
• When its interesting
• Last year (S5) for the Crab! (Pitkin talk)
• Where were 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 weve 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
  arXiv0708.3818)
• Best strain upper limit is 2?10-24 (sky
  polarization combo)
• When its interesting
• Already comparable to supernova limit, though
  thats fuzzy

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Unseen neutron stars
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Unseen neutron stars

• What weve 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
  arXiv0708.3818)
• Best strain upper limit is 2?10-24 (sky
  polarization combo)
• When its interesting
• Already comparable to supernova limit, though
  thats fuzzy
• Where were going
• S4 S5 longer datasets (longest coherent
  integration 25 hours)
• Einstein_at_Home now on S5 - like SETI_at_Home but LIGO
  data, download from http//einstein.phys.uwm.edu

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Directed searches

• What were doing
• Cas A (youngest known neutron star?) 10 days S5
• Galactic center (innermost parsec, good place for
  unknowns)
• When its interesting
• Cas A and any 100yr old star in center have hIL
  1?10-24
• Doable with present sensitivity!
• Anything detectable now would require solid quark
  matter

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Directed searches
?IL 10-4?
?IL 10-5?
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Directed searches

• What were doing
• Cas A (youngest known neutron star?) 10 days S5
• Galactic center (innermost parsec, good place for
  unknowns)
• When its interesting
• Cas A and any 100yr old star in center have hIL
  1?10-24
• 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.
  HESS?Chandra) 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 weve 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 3?10-24 at 200Hz
• When its interesting
• 100? lower than that (Watts talk)
• What kills our sensitivity? Not knowing frequency
  (orbit too)
• What were 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
• Cant rule out equations of state (stars could
  just be flat) unless we know mountain building,
  so what builds mountains?
• Interpretation of detections (lets 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 dont see anything until advanced LIGO
• Download Einstein_at_Home!