Interactions between gravitational waves and photon astronomy (periodic signals) Ben Owen October 20, 2007 LSC-VIRGO / NS meeting 1
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 in fl uence 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 October 20, 2007 LSC-VIRGO / NS meeting 2
GW emission mechanisms • Non-accreting stars (indirect limits beatable now !) – Free precession (looks pretty weak, I’ll skip) – Elastic ally supported “ mountains ” - internal too – Magnetic ally 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
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/0702021 – Whole star solid , high density: � < few � 10 -4 • Also Lin PRD 2007, Haskell et al arXiv:0708.2984 October 20, 2007 LSC-VIRGO / NS meeting 4
Elastic mountains in accreting stars Bildsten ApJL 1998, Ushomirsky et al MNRAS 2000 • How to build high mountains? • Non-uniform accretion fl ow � hot & cold spots on crust Hot spot at fi xed density � • faster electron capture � layer of denser nuclei moves upward ( non-barotropic EOS ) • If GW balance accretion, � is determined by x-ray fl ux • 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
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
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 in fi nite 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
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 October 20, 2007 LSC-VIRGO / NS meeting 8
Indirect upper limits • Accreting stars - energy conservation violated – Assume accretion spin-up = GW spin-down (Wagoner ApJL 1984) – Infer accretion rate from x-ray fl ux – 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) October 20, 2007 LSC-VIRGO / NS meeting 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 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) October 20, 2007 LSC-VIRGO / NS meeting 10
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 October 20, 2007 LSC-VIRGO / NS meeting 11
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 3 � 10 -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 October 20, 2007 LSC-VIRGO / NS meeting 12
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 2 � 10 -24 (sky & polarization combo) • When it’s interesting: – Already comparable to supernova limit, though that’s fuzzy October 20, 2007 LSC-VIRGO / NS meeting 13
Unseen neutron stars October 20, 2007 LSC-VIRGO / NS meeting 14
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 2 � 10 -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 October 20, 2007 LSC-VIRGO / NS meeting 15
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 ~ 1 � 10 -24 – Doable with present sensitivity! – Anything detectable now would require solid quark matter October 20, 2007 LSC-VIRGO / NS meeting 16
Directed searches � IL = 10 -4 � � IL = 10 -5 � October 20, 2007 LSC-VIRGO / NS meeting 17
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 ~ 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 October 20, 2007 LSC-VIRGO / NS meeting 18
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 3 � 10 -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) October 20, 2007 LSC-VIRGO / NS meeting 19
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), fi rming up with Chandra or Hubble would help our searches October 20, 2007 LSC-VIRGO / NS meeting 20
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