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Interactions between gravitational waves and photon astronomy (periodic signals)PowerPoint Presentation

Interactions between gravitational waves and photon astronomy (periodic signals)

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### Interactions between gravitational waves and photon astronomy(periodic signals)

Ben Owen

LSC-VIRGO / NS meeting

Intro astronomy

- 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

LSC-VIRGO / NS meeting

GW emission mechanisms astronomy

- 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

LSC-VIRGO / NS meeting

Elastic mountains astronomy

- 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

LSC-VIRGO / NS meeting

Elastic mountains in accreting stars astronomy

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 few10-7, same as predicted max for normal neutron star crust

LSC-VIRGO / NS meeting

R-modes in accreting stars astronomy

- 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)

LSC-VIRGO / NS meeting

Four types of neutron stars astronomy

(P>50ms 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

LSC-VIRGO / NS meeting

Indirect upper limits astronomy

- 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

LSC-VIRGO / NS meeting

Indirect upper limits astronomy

- 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)

LSC-VIRGO / NS meeting

Known pulsars astronomy

- 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)

LSC-VIRGO / NS meeting

Known pulsars astronomy

Crab, IL = 710-4

J1952+3252, IL = 110-4

95% confidence threshold

by end of S5

J0537-6910, IL = 910-5

LSC-VIRGO / NS meeting

Known pulsars astronomy

- 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

LSC-VIRGO / NS meeting

Unseen neutron stars astronomy

- What we’ve published:
- S210 hours coherent search (Abbott et al gr-qc/0605028)
- S2few weeks semi-coherent search (Abbott et al 2005)
- S4few 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

LSC-VIRGO / NS meeting

Unseen neutron stars astronomy

LSC-VIRGO / NS meeting

Unseen neutron stars astronomy

- What we’ve published:
- S210 hours coherent search (Abbott et al gr-qc/0605028)
- S2few weeks semi-coherent search (Abbott et al 2005)
- S4few 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

LSC-VIRGO / NS meeting

Directed searches astronomy

- 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

LSC-VIRGO / NS meeting

Directed searches astronomy

- 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

LSC-VIRGO / NS meeting

Accreting neutron stars in LMXBs astronomy

- What we’ve published (Sco X-1):
- S26 hours coherent integration (Abbott et algr-qc/0605028)
- S420 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)

LSC-VIRGO / NS meeting

Observational interactions astronomy

- 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

LSC-VIRGO / NS meeting

Theory(-ish) interactions astronomy

- 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?

LSC-VIRGO / NS meeting

Wrap astronomy

- 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!

LSC-VIRGO / NS meeting

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