How photon astronomy affects searches for continuous gravitational waves

1. How photon astronomy affects searches for continuous gravitational waves Ben Owen Gravitational Wave Data Analysis Workshop

2. Several ways • 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 • Theories of neutron star formation and GW emission mechanisms affect where we look • Our interpretation of our results depends on emission mechanisms and indirect upper limits • Some review in Abbott et al, PRD 76, 082001 (2007) Gravitational Wave Data Analysis Workshop

3. Four types of search • Known pulsars (e.g. Crab) • Position & frequency evolution known (including derivatives, timing noise, glitches, orbit)  Computationally inexpensive • Unseen neutron stars (???) • Nothing known, search over position, frequency & its derivatives  Could use infinite computing power, must do sub-optimally • Accreting neutron stars (LMXBs, 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 Gravitational Wave Data Analysis Workshop

4. Indirect upper limits on GW amplitude • Direct limits are always interesting at some level, but much more interesting if they beat indirect limits… • Known pulsars - “spin-down limit” assumes all df/dt is due to GW emission: • Highest in initial LIGO frequency band is Crab at 1.410-24 • Up by ~2 if you push uncertainties in I and D • Directed searches - same & substitute age = t=f/(4|df/dt|) • Highest well-determined one is Cas A at 1.210-24 • We don’t know if it’s in the LIGO frequency band Gravitational Wave Data Analysis Workshop

5. Indirect upper limits on GW amplitude • Accreting stars in LMXBs - assume accretion/GW torque balance & take x-ray flux as proxy for accretion rate • Highest is Sco X-1 at 110-26 • Unseen neutron stars - use supernova rate in galaxy & plug into statistical population model • Most optimistic estimate is 410-24 • Statistical estimate with huge uncertainties Gravitational Wave Data Analysis Workshop

6. If you know what you’re looking for, it’s easier to find it • Coherent integration gains signal-to-noise as T1/2 • OK if you know sky position, frequency, derivatives, … • If you don’t know, integrate for each possible parameter value • Cost may scale as up to T7, so T is computationally limited • Incoherent combination of N coherent pieces gains as N1/4 • Scaling and overall factor depend on parameter space searched - smaller is better! Gravitational Wave Data Analysis Workshop

7. 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 PRL 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 (few weeks of data) • When it gets interesting: • Last year (S5) for the Crab! Paper soon… Gravitational Wave Data Analysis Workshop

8. Known pulsars Crab, IL = 710-4 J1952+3252, IL = 110-4 95% confidence threshold by end of S5 J0537-6910, IL = 910-5 Gravitational Wave Data Analysis Workshop

9. 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 PRL 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 (few weeks of data) • When it’s interesting: • Last year (S5) for the Crab!Paper soon… • 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 Gravitational Wave Data Analysis Workshop

10. Unseen neutron stars (see next 2 talks) • What we’ve published: • S210 hours coherent search (Abbott et al PRD 2007) • S2few weeks semi-coherent search (Abbott et al PRD 2005) • S4few weeks semi-coherent searches (Abbott et al arXiv:0708.3818) • Best strain upper limit is 210-24 • When it’s interesting: • Already comparable to supernova limit, though that’s fuzzy • Where we’re going: • S5few months (longest coherent integration 25 hours) • Einstein@Home now on S5 - like SETI@Home but LIGO data, download from http://einstein.phys.uwm.edu ! Gravitational Wave Data Analysis Workshop

11. Accreting neutron stars • What we’ve published (Sco X-1): • S26 hours coherent integration (Abbott et alPRD 2007) • S420 days incoherent “radiometer” (Abbott et al PRD 2007) • Best strain upper limit is 310-24 at 200Hz • When it’s interesting: • 100 lower than that: tricky even with advanced LIGO • What we’re doing: • Working on better analysis methods • Looking at other sources (frequency is known for some) • Coordinating with RXTE (Markowitz poster) & cheering AstroSat Gravitational Wave Data Analysis Workshop

12. Directed searches • What we’re doing: • Cas A (youngest known neutron star?) ~2 weeks S5 • Galactic center (innermost parsec, good place for unknowns) • When it’s interesting: • Cas A and any ~100yr old star in center have hIL ~ 110-24 • Doable with present sensitivity! Gravitational Wave Data Analysis Workshop

13. Directed searches IL = 10-4 IL = 10-5 Gravitational Wave Data Analysis Workshop

14. Directed searches • What we’re doing: • Cas A (youngest known neutron star?) ~2 weeks S5 • Galactic center (innermost parsec, good place for unknowns) • When it’s interesting: • Cas A and any ~100yr old star in center have hIL ~ 110-24 • Doable with present sensitivity! • 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 … Gravitational Wave Data Analysis Workshop

15. 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 PSRs/CCOs/etc, think of indirect GW limits • Old discoveries • Several NS positions are poorly known (ROSAT/XMM), firming up with Chandra or Hubble would help our searches Gravitational Wave Data Analysis Workshop

16. Theory(-ish) interactions • Where do we look? • Sky positions likely to have young neutron stars • What frequencies are emitted by LMXBs? • Interpretation of upper limits (right now) • How fuzzy are indirect limits? Distances, braking indices… • Can not rule out equations of state (stars could just be flat) unless we know about mountain building, so what builds mountains? • Interpretation of detections (let’s hope it’s soon!) • High ellipticity means funny equation of state • Somewhat high  means EOS or high internal B field: which? • Frequency reveals emission mechanism, composition (AMSPs) Gravitational Wave Data Analysis Workshop

17. 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 - party’s just starting! Gravitational Wave Data Analysis Workshop