Published on October 3, 2007
What science can initial LIGO do with pulsars?: What science can initial LIGO do with pulsars? Ben Owen Detections or upper limits: Detections or upper limits New emission mechanisms Magnetic mountains Magnetic bottling Mountains all the way down Types of searches Known pulsars (radio) Low-mass x-ray binaries X-ray point sources Unknown objects Owen in Amaldi “Old” emission mechanisms: “Old” emission mechanisms Key number is “ellipticity” From moment of inertia: = (Ixx - Iyy)/Izz Roughly quadrupole/inertia or R/R Standard answer: < few 10-7 Observation of x-ray binaries Theory of mountains in crust, r-modes, … Since h ~ , this means advanced LIGO Free precession is OK for advanced LIGO too Magnetic mountains: Magnetic mountains Cutler PRD 2002 Differential rotation creates toroidal field Field pinches star Rotation spreads star Stable when winding axis orthogonal to rotation axis (cigar) Flip timescale determined by crust Magnetic mountains: Magnetic mountains Max > 10-5 , but… Observations say flip doesn’t go all the way B field pops out if wound too tight (1016G? Magnetars?) B field diffuses through resistive matter if too high-lifetime? Magnetic bottling: Magnetic bottling Melatos & Payne MNRAS 2005 Accreting millisecond pulsars: B ~ 108 G Accreted plasma/metal conducts electricity Crosses B field lines slowly (resistivity) Funneled and bottled at poles by field Magnetic bottling: Magnetic bottling Can’t have B >> 108 G (field repels) Need high accretion rate to build mountain But that heats matter, reduces conductivity Max. 10-5 for observed B fields But needs T = 107 K (hard to get) And makes x-rays… Mountains all the way down: Mountains all the way down Owen PRL next week Strange quark stars might be all solid Quark-baryon hybrids might have solid cores Meson condensates too (generic mechanism) Order of magnitude is calculable (surprise!) Mountains all the way down: Mountains all the way down Quark stars < few 10-4 Hybrid stars < 10-5 Meson stars < 10-5 Highly dependent on poorly explored parameters How to drive mountains to maximum height? Known pulsar search: Known pulsar search Known signal phase means matched filtering, including Doppler shifts from LIGO motion Radio is the only timing data good enough Abbott et al. PRL 2005: 28 isolated pulsars, some S2 upper limits were < 10-5 But radio spindown puts better limits so far d/dt = 8.5 10-13 (/50Hz)5 (/10-5)2 Spindown < 10-8 for old millisecond pulsars Young ones should be different population… Known pulsar search: Known pulsar search Sensitivity goes as hrms T1/2 S6: cut 3 yr to 1.5 yr for 2 upgrade in hrms? J0534+2200 (Crab) at 60 Hz, 2 kpc Spindown = 7.4 10-4 S5 1 yr gets 1.1 10-4, upgrade gets 4.6 10-4 J1952+3252 (CTB 80) at 50 Hz, 2.5 kpc Spindown = 1.1 10-4 Upgrade gets 9 10-5 (J1913+1011 still missed by 2 with upgrade) Known pulsar search: Known pulsar search Pulsars in globular clusters: Generally older, further away, thus worse But some spin-downs are questionable (spin-up!) Masked by cluster dynamics ~ 10-14 Hz/s J2129+1210D in M15 at 5 10-13 Hz/s Check ANTF catalogue: 90 in globular clusters 4 or so with maskable spindown (25-50 Hz) Low-mass x-ray binaries: Low-mass x-ray binaries Accretion spin-up = GW spin-down means ellipticity given by x-ray flux Implies < few 10-7 for known ones, GW too faint for initial detectors Any =10-5 must be unseen for some reason Data analysis: computationally limited because of poorly known phase: frequency, orbit, accretion random walk X-ray point sources: X-ray point sources Like Cas A Doppler shifts known Spindown unknown, could be very large Coherent integration OK up to few weeks (courtroom notes) Just getting started List of candidates? Unknown objects: Unknown objects All-sky, all-frequency: biggest CPU sink, can’t do full matched filtering But try http://einstein.phys.uwm.edu/ Sensitivity scales as T1/4 or so, favors upgrade Abbott et al. gr-qc/0508065 and upcoming Can’t untangle ellipticity from distance without proper motion frequency shift & advanced LIGO (Seto PRD 2005) Could get GW fraction of spindown (me) So what’s the answer?: So what’s the answer? Detect high ellipticity Only untangled from distance for known pulsars or (some) x-ray point sources Means not a normal neutron star Non-detections (upper limits) Known: Can’t rule out a matter model, though many (advanced) could weigh against it Unknowns: How to phrase exclusion region? Start making galactic population synthesis?