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A New Relativistic Binary Pulsar: Gravitational Wave Detection and Neutron Star Formation Vicky Kalogera Physics & Astronomy Dept with Chunglee Kim (NU) Duncan Lorimer (Manchester) Bart Willems (NU) Mia Ihm (NU)

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In this talk : In this talk : Gravitational Waves and Double Neutron Stars Gravitational Waves and Double Neutron Stars Meet PSR J : Meet PSR J : the most relativistic binary and the most relativistic binary and the first double pulsar the first double pulsar Inspiral Event Rates Inspiral Event Rates for NS-NS, BH-NS, BH-BH for NS-NS, BH-NS, BH-BH Supernovae and NS-NS Formation Supernovae and NS-NS Formation

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Global network of GW detectors LIGO GEO VIRGO TAMA AIGO

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Binary Compact Object Inspiral Do they exist ? YES! Prototype NS -NS: binary radio pulsar PSR B What kind of signal ? inspiral chirp GW emission causes orbital shrinkage leading to higher GW frequency and amplitude orbital decay PSR B Weisberg & Taylor 03

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Sensitivity to coalescing binaries What is the expected detection rate out to D max ? Scaling up from the Galactic rate detection rate ~ r 3 strength ~ 1/r D max for each signal sets limits on the possible detection rate

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Inspiral Rates for the Milky Way Theoretical Estimates Based on models of binary evolution until binary compact objects form. for NS -NS, BH -NS, and BH -BH Empirical Estimates Based on radio pulsar properties and survey selection effects. for NS -NS only

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Properties of known coalescing DNS pulsars B B C M15 (NGC 7078) Galactic Disk pulsars J Burgay et al. 2003

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Properties of known coalescing DNS pulsars B x B x J x C x M15 (NGC 7078) Galactic Disk pulsars P s (ms) (ss -1 ) L 400 PsPs. Burgay et al. 2003

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Properties of known coalescing DNS pulsars B x B x J x C x M15 (NGC 7078) Galactic Disk pulsars P s (ms) (ss -1 ) L 400 B 9 (G) PsPs. Burgay et al. 2003

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Properties of known coalescing DNS pulsars B x B x J x C x M15 (NGC 7078) Galactic Disk pulsars P s (ms) (ss -1 ) L 400 B 9 (G) d(kpc) PsPs. Burgay et al. 2003

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Properties of known coalescing DNS pulsars M15 (NGC 7078) Galactic Disk pulsars B x B x J x P s (ms) (ss -1 ) P orb (hr) PsPs C x Burgay et al. 2003

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Properties of known coalescing DNS pulsars M15 (NGC 7078) Galactic Disk pulsars B x B x J x P s (ms) (ss -1 ) P orb (hr) e PsPs C x Burgay et al. 2003

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Properties of known coalescing DNS pulsars M15 (NGC 7078) Galactic Disk pulsars B x (1.39) B x (1.35) J x (1.24) P s (ms) (ss -1 ) P orb (hr) e M tot ( ) PsPs. MoMo C x (1.36) Burgay et al. 2003

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Properties of known coalescing DNS pulsars B º.23 B º.75 J º C º.46 M15 (NGC 7078) Galactic Disk pulsars c (Myr) sd (Myr) mrg (Myr) (yr -1 ) · Burgay et al. 2003

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animation credit: John Rowe PSR J A and B in motion!

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Radio Pulsars in NS-NS binaries NS-NS Merger Rate Estimates Use of observed sample and models for PSR survey selection effects: estimates of total NS- NS number combined with lifetime estimates (Narayan et al. '91; Phinney '91) Dominant sources of rate estimate uncertainties identified: (VK, Narayan, Spergel, Taylor '01) small - number observed sample (2 NS - NS in Galactic field) PSR population dominated by faint objects Robust lower limit for the MW (10 -6 per yr) Upward correction factor for faint PSRs: ~ X 3

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small-N sample is: > assumed to be representative of the Galactic population > dominated by bright pulsars, detectable to large distances total pulsar number is underestimated pulsar luminosity function: ~ L -2 i.e., dominated by faint, hard-to-detect pulsars NGNG N est median 25% (VK, Narayan, Spergel, Taylor '01)

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Radio Pulsars in NS-NS binaries NS-NS Merger Rate Estimates (Kim, VK, Lorimer 2002) It is possible to assign statistical significance to NS-NS rate estimates with Monte Carlo simulations Bayesian analysis developed to derive the probability density of NS-NS inspiral rate Small number bias and selection effects for faint pulsars are implicitly included in our method.

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Statistical Method pulse and orbital properties similar to each of the observed DNS 1.Identify sub-populations of PSRs with pulse and orbital properties similar to each of the observed DNS Model each sub-population in the Galaxy with Monte-Carlo generations Luminosity distribution Luminosity distribution Spatial distribution Spatial distribution power-law: f(L) L -p, L min < L (L min : cut-off luminosity) 2. Pulsar-survey simulation consider selection effects of all pulsar surveys consider selection effects of all pulsar surveys generate ``observed’’ samples generate ``observed’’ samples

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fill a model galaxy with N tot pulsars count the number of pulsars observed (N obs ) Earth Statistical Method 3. Derive rate estimate probability distribution P(R)

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Statistical Analysis given total number of For a given total number of pulsars pulsars, N obs follows Poisson distribution. a Poisson distribution. best-fit We calculate the best-fit value of P(1; N tot ) value of as a function of N tot and the probability P(1; N tot ) We use Bayes ’ theorem to calculate P(N tot ) and finally P(R) P(N obs ) for PSR B

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Results: P(R tot ) most probable rate R peak statistical confidence levels expected GW detection rates

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Current Rate Predictions 3 NS-NS : a factor of 6-7 rate increase Initial LIGO Adv. LIGO per 1000 yr per yr ref model: peak % Burgay et al. 2003, Nature, 426, 531 VK et al. 2004, ApJ Letters, in press opt model: peak %

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Results: R peak vs model parameters

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Current expectations for LIGO II (LIGO I) detection rates of inspiral events NS -NS BH -NS BH -BH D max (Mpc) (20) (40) (100) R det ,000 (1/yr) ( ) (3x ) (4x ) from population synthesis Use empirical NS-NS rates:constrain pop syn models > BH inspiral rates

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NS-NS Formation Channel from Tauris & van den Heuvel 2003 How was PSR J formed ? current properties constrain NS #2 formation process: NS kick NS progenitor

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NS-NS Formation Channel animation credit: John Rowe

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Willems & VK 2004 X X orbital period (hr)eccentricity Evolve the system backwards in time… GR evolution back to post-SN #2 properties: N.B. time since SN #2 can be set equal to > the spin-down age from maximum spin-up: ~100Myr (Arzoumanian et al. 2001)

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Willems & VK 2004 Evolve the system backwards in time… Constraints on pre-SN #2 properties: post-SN orbit must contain pre-SN position (in circular orbit): A (1-e) < A o < A (1+e)

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Willems & VK 2004 Evolve the system backwards in time… Constraints on pre-SN #2 properties: post-SN orbit must contain pre-SN position (in circular orbit): A (1-e) < A o < A (1+e) NS #2 progenitor: helium star to avoid mass transfer: A o > A min = R HE max / r L

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Willems & VK 2004 Evolve the system backwards in time… Constraints on pre-SN #2 properties: post-SN orbit must contain pre-SN position (in circular orbit): A (1-e) < A o < A (1+e) NS #2 progenitor: helium star to avoid mass transfer: A o > A min = R HE max / r L to satisfy post-SN masses, a, e: M o < M max = f(V k ) M o > 20 M solar and V k > 1215 km/s unlikely …

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Willems & VK 2004 Evolve the system backwards in time… Constraints on pre-SN #2 properties - allow for mass transfer from the He star: post-SN orbit must contain pre-SN position (in circular orbit): A (1-e) < A o < A (1+e)

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Willems & VK 2003 Evolve the system backwards in time… Constraints on pre-SN #2 properties - allow for mass transfer from the He star: post-SN orbit must contain pre-SN position (in circular orbit): A (1-e) < A o < A (1+e) to form a NS: M o > 2.1 M solar Habets 1986

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Willems & VK 2004 Evolve the system backwards in time… Constraints on pre-SN #2 properties - allow for mass transfer from the He star: post-SN orbit must contain pre-SN position (in circular orbit): A (1-e) < A o < A (1+e) to form a NS: M o > 2.1 M solar to avoid a merger: M o < 3.5 M PSR = 4.7 M solar Ivanova et al Habets 1986

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Willems & VK 2004 Evolve the system backwards in time… Constraints on pre-SN #2 properties - allow for mass transfer from the He star: post-SN orbit must contain pre-SN position (in circular orbit): A (1-e) < A o < A (1+e) to form a NS: M o > 2.1 M solar to avoid a merger: M o < 3.5 M PSR = 4.7 M solar to satisfy post-SN masses, a, e: M o < M max = f(V k ) 2.1 < M o < 4.7 M solar V k > 60 km/s Habets 1986 Ivanova et al. 2003

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Willems & VK 2004 What is the probability distribution of the natal kick imparted to NS #2 ? Assumption: isotropic natal kicks

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Willems & VK 2004 What is the probability distribution of the natal kick imparted to NS #2 ? insensitive to progenitor mass uncertainties

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Willems & VK 2004 What is the probability distribution of the natal kick imparted to NS #2 ? insensitive to NS age uncertainties

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Willems & VK 2004 What is the probability distribution of the natal kick imparted to NS #2 ? additional constraints from center-of-mass velocity measurements (Willems, VK, Henninger, in prep.)

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(Ihm, VK & Belczynski, in prep) Probability distribution of post-SN orbital characteristics o o o o o o Are tight binaries with low eccentricity surprising ?

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What have we learned already from PSR J (A and B) ? Burgay et al Lyne et al Inspiral detection rates as high as 1 per 1.5 yr (at 95% C.L.) are possible for initial LIGO Detection rates in the range per yr are most probable for advanced LIGO (VK, Kim, Lorimer, et al. 2004) PSR-B progenitor is constrained to be less massive than ~5 M solar PSR-B kick is constrained to be in the range km/s the most probable isotropic magnitude is 150 km/s (Willems & VK 2004) PSR-A eclipses: magnetosphere physics PSR-B is torqued by PSR-A (Kaspi et al. 2004) PSR-A and B polarimetry: A’s beam is a very wide hollow cone A’s spin and magnetic axes nearly aligned (Demorest et al. 2004)

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What will we learn in the near future ? center-of-mass velocity measurements (Ransom et al.) --> tighter constraints on NS formation --> PSR-A precession predictions (spin-tilt angle and disappearence) (Willems, VK, & Henninger) better confirmation of GR new relativistic effects ? better understanding of PSR magnetospheres ? complete understanding of double PSR geometry --> PSR-A precession predictions (Jenet & Ransom) constraints of NS-NS population characteristics and binary evolution (Ihm, VK & Belczynski)

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Parkes MultiBeam survey and acceleration searches Assuming that acceleration searches can perfectly correct for any pulse Doppler smearing due to orbital motion… How many coalescing DNS pulsars would we expect the PMB survey to detect ? VK, Kim et al PMB N obs = 3.6 N.B. Not every new coalescing DNS pulsar will significantly increase the DNS rates …

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