1. Expected Coalescence Rate of NS/NS Binaries for Ground Based Interferometers Tania Regimbau OCA/ARTEMIS on the behalf of J.A. de Freitas Pacheco, T. Regimbau, S. Vincent, A. Spallicci

2. The Model  a very small fraction of massive binaries remains bounded after 2 supernova explosions  the resulting system consist of: 1. a partially reaccelerated pulsar 2. a young pulsar with - same period evolution (magnetic dipole spin down) as normal radio pulsars - same kick velocity as millisecond pulsars (for which the supernova didn’t disrupt the system either)

3. The Galactic Coalescence Rate

4. The Galactic Star Formation Rate previous studies: the star formation rate is proportional to the available mass of gas as, R * (t) ~ e -  t present work: the star formation history is reconstructed from observations:  ages of 552 stars derived from chromospheric activity index (Rocha-Tinto et al., 2000)  enhanced periods of star formation at 1 Gyr, 2-5 Gyr and 7- 9 Gyr probably associated with accretion and merger episodes from which the disk grows and acquires angular momentum (Peirani, Mohayaee, de Freitas Pacheco, 2004)

5. The Galactic Coalescence Rate

6. Numerical Simulations (P(  ),  0,  NS )  initial parameters:  masses: M 1, Salpeter IMF, M 1 /M 2 : probability derived from observations  separation: P(a)da=da/a between 2R Roche and 200R Roche  eccentricity: P(e)de = 2ede  evolution of orbital parameters due to mass loss (stellar wind, mass transfert, supernova)  statistical properties   NS = 2.4% (systems that remain bounded after the second supernova)  P(  0.087/  probability for a newly formed system to coalesce in a timescale      2x10 5 yr (minimum coalescence time) Vincent, 2002 birth parameters (M1, M2, a, e) 0 Mass loss (M1, M2, a, e) 1 Supernova 1 disrupted NS/NS system a, e ->  Mass loss (1.4Mo, M2, a, e) 2 Supernova 2 disrupted E > 0

7. The Galactic Coalescence Rate

8. Population Synthesis (f b ) birth parameters P o, B o, v k, d o … magnetic braking selection effects: sky coverage, cone, flux observedhidden present properties P, dP/dt, d, S … +-  single radio pulsar properties: N p = 250000 (for 1095 observed) birth properties  second binary pulsar properties: the youngest pulsar has the same: - period evolution (magnetic dipole spin down) as single radio pulsars - kick velocity as millisecond pulsars (remains bounded after the supernova) Nb = 730 (for two observed)  3.6 ± 0.211 ± 0.5 ln  0 (s) 80± 20240 ± 20P 0 (ms) dispertionmean Regimbau, 2001&2004

9. The Local Coalescence Rate  weighted average over spiral (f S =65%) and elliptical (f E =35%) galaxies  same f b and  NS as for the Milky Way  spiral galaxy coalescence rate equal to the Milky Way rate:  S = MW = (1.7±1)x10 -5 yr -1  elliptical galaxy star formation efficiency and IMF estimated from observations - color & metallicity indices (Idiart, Michard & de Freitas Pacheco, 2003)  E =  8.6x10 -5 yr -1  c = 3.4x10 -5 yr -1 other estimates: ~10 -6 – 10 -4 yr -1 (Kalogera et al., 2004: 1.8x10 -4 yr -1 ) Intermitent star formation history: modulation in the coalescence rate Bulk of stars formed in the first 1-2 Gyr. The pairs merging today were formed with long coalescence times (P  ~1/  )

10.  coalescence rate within the volume V=4/3  D 3 counts of galaxies from the LEDA catalog: - 10 6 galaxies (completness of 84% up to B = 14.5) - inclusion of the Great Attractor (intersection of Centaurus Wall and Norma Supercluster) corresponding to 4423 galaxies at Vz = 4844 km/s The Detection Rate  maximum probed distance and mean expected rate (S/N=7; false alarm rate=1) : VIRGOLIGOLIGO Ad 13 Mpc 1 event/148 yr 14 Mpc 1 event /125 yr 207 Mpc 6 events/yr

11. Possible Improvements in the Sensitivity…  gain in the VIRGO thermal mirror noise band (52-148 Hz): reduction of all noises in the band by a factor 10 (Spallicci, 2003; Spallicci et al., submitted) gain throughout VIRGO full bandwidth reduction of pendulum noise by a factor 28, thermal mirror 7, shot 4 (Punturo, 2004; Spallicci et al., submitted) maximum probed distance: 100 Mpc detection rate: 1.5 events / yr  use networks of detectors: LIGO-H/LIGO-L/VIRGO(Pai, Dhurandhar & Bose, 2004) false alarm rate = 1, detection probability = 95% maximum probed distance: 22 Mpc detection rate: 1 events / 26 yrs

12. Work in progress  compute the GW stochastic background produced by the superposition of all the NS/NS binaries  analytical approach integration up to to z~6  numerical approach generating extragalactic populations of NS/NS binaries

13. Extra slides

14. .. PSR J0737-3039 A+B AB P dP/dt Bsurf 22.7 ms 1.7 x 10 -18 6 x 10 9 G 2.77 s 0.88 x 10 -15 1.6 x 10 12 G

15. Kalogera, Kim, Lorimer et al., 2004  Numerical simulations sample of 3 galactic coalescing pulsars, (P, dP/dt) i populate a model galaxy (P(L, R, z)) with Ntot pulsars with (P, dP/dt) i model radiotelescope survey selection effects and compute Nobs i  Statistics Nobs i follows a Poisson distribution of mean i i =  i Ntot bayesian statistic to compute P i (Ntot)  coalescence rate R i = Ntot i /  life f b P(R i ) with mean and confidence level combine P(R i ) to obtain P(R)