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Binary Neutron Star Mergers Gravitational-Wave Sources and Gamma-Ray Bursts

Binary Neutron Star Mergers Gravitational-Wave Sources and Gamma-Ray Bursts. Vicky Kalogera Dept. of Physics & Astronomy Northwestern University. Binary Compact Objects. In this talk:. Double Neutron Stars: the sample Two new DNS binaries! Empirical DNS rates: updates

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Binary Neutron Star Mergers Gravitational-Wave Sources and Gamma-Ray Bursts

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  1. Binary Neutron Star MergersGravitational-Wave SourcesandGamma-Ray Bursts Vicky Kalogera Dept. of Physics & Astronomy Northwestern University

  2. Binary Compact Objects In this talk: • Double Neutron Stars: the sample • Two new DNS binaries! • Empirical DNS rates: updates • Theoretical Merger Rates • Constraining population syntheses • Expectations for LIGO - when??? • NS mergers and short GRBs? • Merger delays and redshift distributions

  3. GW orbital decay PSR B1913+16 Weisberg & Taylor 03 DNS pulsars: Hulse-Taylor Indirect evidence for Gravitational Waves pulsar as a `lighthouse'

  4. Coincidence: detection confidence source localization LIGO Virgo GEO signal polarization TAMA Direct detection? GW Interferometers: global network AIGO

  5. Double Neutron Star (DNS) Systems one of the prime targets of large-scale GW detectors (e.g. LIGO, VIRGO, GEO, TAMA) Event rate estimation for DNS inspiral search Galactic merger rate of DNS systems Development and designing of GW detectors Understanding of the astrophysics of compact objects Strong sources of gravitational waves (waveforms are well understood)

  6. DNS merger rate calculations Empirical method: based onradio pulsar propertiesandobservational selection effects of pulsar surveys (Narayan et al. (1991), Phinney (1991), Curran & Lorimer (1993), VK, Narayan et al. (2001), Kim, VK et al. (2003), VK, Kim et al. (2004)) Theoretical method: based on our understanding of binary formation and evolution (population synthesis models) (Portegies Zwart & Yungelson (1998), Nelemans et al. (2001), Belczynski, VK, & Bulik (2002), O’Shaughnessy, VK et al. (2005) and many more)

  7. DNS pulsars: the observed sample PSR name Ps (ms) Pb (hr) e life (Gyr) B1913+16 59.03 7.752 0.617 0.365 B1534+12 37.90 10.1 0.274 2.7 J0737-3039A 22.70 2.45 0.088 0.185 J1756-2251 28.46 7.67 0.181 2.0 J1906+0748 144.07 3.98 0.085 0.083 Burgay et al. 2003 Parkes double pulsar Faulkner et al. 2004 Parkes MB survey, acceleration search Lorimer et al. 2005 Arecibo ALFA survey

  8. Merger rate R beaming Number of sources x correction factor R = Lifetime of a system Q: How many pulsars “similar” to each of the known DNS binaries exist in our Galaxy? Goal : Calculate the probability distribution of the Galactic DNS merger rates P(R)

  9. Method - Modeling & Simulation (Kim et al. 2003, ApJ, 584, 985 ) • adapt spin & orbital periods from each observed PSR • assume luminosity & spatial distribution functions 1. Model pulsar sub-populations Selection effects for faint pulsars are taken into account.

  10. Method - Modeling & Simulation (Kim et al. 2003, ApJ, 584, 985 ) Earth 2. Simulate large-scale pulsar surveys populate a model galaxy with Npop PSRs (same Ps & Porb) count the number of pulsars observed (Nobs) Nobs follows the Poisson distribution, P(Nobs; <Nobs>) carefully model thresholds of PSR surveys

  11. Statistical Analysis <Nobs>life i Npopfb  Individual probability density function (PDF) For an each observed system i, Pi(R) = Ci2R exp(-CiR) where Ci =  Combine the three individual PDFs and calculate P(Rgal)

  12. Probability density function of Rgal P(Rgal ) Lifetime ~ 80 Myr (shortest) NJ1906 ~ 300 Lifetime ~ 185 Myr NJ0737 ~ 1600 (most abundant)

  13. The revised DNS merger rate +40 -11 Increase rate factor due to PSR J0737-3039: Increase rate factor due to PSR J1906+0746: Rpeak (revised) Rpeak (revised) ~ 6-7 ~1.5-1.7 Rpeak (previous) Rpeak (previous) Reference model: rate per Myr B1913+B1534+J0737+J1906 B1913+B1534+J0737 B1913+B1534 (at 95% CL) ~120 +209 ~83 ~13 -66

  14. Detection rate of DNS inspirals for LIGO Rdet(ini. LIGO) ~ 1 event per 20 yr Rdet (adv. LIGO) ~ 350 events per yr The most probable DNS inspiral detection rates for LIGO Reference model: All models: Rdet(ini. LIGO) ~ 1 event per 5 – 250 yr Rdet (adv. LIGO) ~ 15 – 850 events per yr

  15. Implications of J1756-2251  Contribution of J1756-2251 to the Galactic DNS merger rate. Rpeak (4 PSRs + J1756) ~ 1.04 No significant change in the total rate. Rpeak (4 PSRs) • J1756-2251: Another merging DNS in the Galactic disk Similar to the Hulse-Taylor system (Faulkner et al. 2005)  Discovered by the Parkes Multibeam Pulsar Survey with the acceleration search technique. Standard Fourier techniques failed to detect J1756-2251.

  16. Global P(Rgal): motivation Rpeak (Myr-1) Lmin (mJy kpc2) p Radio pulsar luminosity function f(L)  L-p, where Lmin is a cut-off luminosity and p is a power index.

  17. Global P(Rgal): motivation Global probability density function Pglobal(R) P(R; Lmin,p) f(Lmin) g(p) intrinsic functions for Lmin and p Pglobal(R) Radio pulsar luminosity function f(L)  L-p , where Lmin is a cut-off luminosity and p is a power index. Rpeak is strongly dependent on Lmin & p. P(R)  P(R; Lmin,p)

  18. Global P(Rgal) and SNe rate constraints The empirical SNe rate SN Ib/c = 600-1600 Myr-1 (Cappellaro, Evans, & Turatto 1999) Suppose, ~5% of Ib/c SNe are involved in the DNS formation. SNL5= SN (lower)x0.05 = 30 Myr-1 SNU5= SN (upper)x0.05 = 80 Myr -1 Probability Density SNU5 SNL5 Galactic DNS merger rate (Myr-1)

  19. Compact Binary Inspiral Rates: What about Black Hole Binaries? • BH-NS binaries could in principle be detected as binary pulsars, BUT… the majority of NS in BH-NS are expected to be young short-lived hard-to-detect harder to detect than NS-NS by >~10-100 ! So far, inspiral rate predictions only from population calculations with uncertainties of ~ 3 orders of mag We can use NS-NS empirical rates as constraints on population synthesis models

  20. Binary Compact Objects: Formation Massive primordial binary Mass-transfer #1: hydrostatically and thermally Stable, but Non-Conservative: mass and A.M. loss Supernova and NS Formation #1: Mass Loss and Natal Kick High-mass X-ray Binary: NS Accretion from Massive Companion’s Stellar Wind Mass-transfer #3: Dynamically Unstable Mass-tranfer #4: Possible and Stable Supernova and NS Formation #2: Mass Loss and Natal Kick Double Neutron-Star Formed! from Tauris & van den Heuvel 2003

  21. Population Synthesis Parameter Study • Large parameter space • Most important parameters: 7 • 7D parameter study: computationally demanding • Acceleration of computations: • Use of Genetic Algorithms

  22. Rate Fits vs. StarTrack calculations: 7D (Belczynski et al. 2005) O’Shaughnessy et al. 2004 BH-BH Fit accuracy is comparable or usually smaller than the Poisson errors of StarTrack Monte Carlo rates NS-NS

  23. BH-NS NS-NS PDF BH-BH log ( events per yr ) Black Hole Binary Inspiral: Event Rates From Population Synthesis Modeling:

  24. Empirical Constraints imposed on population synthesis rate predictions Merging NS-NS Wide NS-NS log(rate) log(rate) O’Shaughnessy et al. 2006

  25. Four More Rate Constraints: O’Shaughnessy et al. 2006 SN Ib/c merging PSR-WD eccentric PSR-WD SN II

  26. Constrained vs. Unconstrained Rate Predictions from StarTrack: O’Shaughnessy et al. 2006 BH-BH BH-NS NS-NS NS-NS BH-BH BH-NS

  27. Short GRBs and NS-NS / BH-NS mergers Short GRB afterglows reveal association with both elliptical and star-forming galaxies: Progenitors must exist in both OLD and YOUNG stellar populations! NS-NS and BH-NS mergers: prime candidates What is the event (GRB and mergers) rate vs. redshift ? What is the spatial distribution w/r to the host galaxies ?

  28. What is the event (GRB and mergers) rate vs. redshift ? We need to know: Star-formation rate vs. redshift Porciani & Madau Time-Delay between formation and mergers Formation efficiency (# mergers / unit SF mass) Relative Contribution of spirals and elliptical galaxies GRB Luminosity function unknown …

  29. ELLIPTICAL GALAXIES NS-NS BH-NS BH-NS log(Merger Time / Myr) Belczynski O’Shaughnessy Time-Delay between formation and mergers SPIRAL GALAXIES NS-NS BH-NS log(Merger Time / Myr)

  30. Belczynski O’Shaughnessy Compact Binary Formation efficiencies What is the number of binaries formed per unit stellar mass? SPIRAL GALAXIES ELLIPTICAL GALAXIES NS-NS NS-NS BH-NS BH-NS log(efficiency * Msun) log(efficiency * Msun)

  31. Merger Rate vs. redshift If ellipticals contributed 20% of the SF mass in the past until about redshift of 2 Comparison with observed redshift distribution requires a luminosity model … ?

  32. Belczynski O’Shaughnessy Binary Center-of-mass velocities and Lifetimes: Where do they merge ? ELLIPTICAL GALAXIES SPIRAL GALAXIES 1kpc 10 kpc NS-NS NS-NS log(Vcm / km/s) log(Vcm / km/s) BH-NS BH-NS log(merger time / Myr) log(merger time / Myr)

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