Interactions between gravitational waves and photon astronomy (periodic signals)

Transcription

1 Interactions between gravitational waves and photon astronomy (periodic signals) Ben Owen October 20, 2007 LSC-VIRGO / NS meeting 1

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/ October 20, 2007 LSC-VIRGO / NS meeting 2

3 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 October 20, 2007 LSC-VIRGO / NS meeting 3

4 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: < 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: < 10-5 Quark star (ad hoc model or color superconductor) Xu ApJL 2003, Mannarelli et al hep-ph/ Whole star solid, high density: < few 10-4 Also Lin PRD 2007, Haskell et al arxiv: October 20, 2007 LSC-VIRGO / NS meeting 4

5 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 October 20, 2007 LSC-VIRGO / NS meeting 5

6 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) October 20, 2007 LSC-VIRGO / NS meeting 6

7 Four types of neutron stars (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 October 20, 2007 LSC-VIRGO / NS meeting 7

8 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 Non-pulsing NS - substitute age = f/(-4df/dt) Best is Cas A at October 20, 2007 LSC-VIRGO / NS meeting 8

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 Unknown neutron stars -??? Assume simple population model Plug in supernova rate in galaxy Most optimistic estimate is (Abbott et al gr-qc/ ) October 20, 2007 LSC-VIRGO / NS meeting 9

10 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 for PSR J When it gets interesting: Last year (S5) for the Crab! (Pitkin talk) October 20, 2007 LSC-VIRGO / NS meeting 10

11 Known pulsars Crab, IL = J , IL = % confidence threshold by end of S5 J , IL = October 20, 2007 LSC-VIRGO / NS meeting 11

12 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 for PSR J 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 October 20, 2007 LSC-VIRGO / NS meeting 12

13 Unseen neutron stars What we ve published: S2 10 hours coherent search (Abbott et al gr-qc/ ) S2 few weeks semi-coherent search (Abbott et al 2005) S4 few weeks semi-coherent searches (Abbott et al arxiv: ) Best strain upper limit is (sky & polarization combo) When it s interesting: Already comparable to supernova limit, though that s fuzzy October 20, 2007 LSC-VIRGO / NS meeting 13

14 Unseen neutron stars October 20, 2007 LSC-VIRGO / NS meeting 14

15 Unseen neutron stars What we ve published: S2 10 hours coherent search (Abbott et al gr-qc/ ) S2 few weeks semi-coherent search (Abbott et al 2005) S4 few weeks semi-coherent searches (Abbott et al arxiv: ) Best strain upper limit is (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 October 20, 2007 LSC-VIRGO / NS meeting 15

16 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 h IL ~ Doable with present sensitivity! Anything detectable now would require solid quark matter October 20, 2007 LSC-VIRGO / NS meeting 16

17 Directed searches IL = 10-4 IL = 10-5 October 20, 2007 LSC-VIRGO / NS meeting 17

18 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 h IL ~ 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 October 20, 2007 LSC-VIRGO / NS meeting 18

19 Accreting neutron stars in LMXBs What we ve published (Sco X-1): S2 6 hours coherent integration (Abbott et al gr-qc/ ) S4 20 days incoherent radiometer (Abbott et al astro-ph/ ) Best strain upper limit is 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) October 20, 2007 LSC-VIRGO / NS meeting 19

20 Observational interactions Timing data for known pulsars Jodrell Bank, several others have agreed to more timing RXTE: J (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 October 20, 2007 LSC-VIRGO / NS meeting 20

21 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? October 20, 2007 LSC-VIRGO / NS meeting 21

22 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! October 20, 2007 LSC-VIRGO / NS meeting 22