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Expected Coalescence Rate of NSNS Binaries for Ground Based Interferometers

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spiral (fS=65%) and elliptical (fE=35%) galaxies. same fb and bNS as for the Milky Way ... elliptical galaxy star formation efficiency and IMF estimated from ... – PowerPoint PPT presentation

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Title: Expected Coalescence Rate of NSNS Binaries for Ground Based Interferometers


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 didnt 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-at
  • 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(t), t0, bNS)
  • initial parameters
  • masses M1, Salpeter IMF, M1/M2 probability
    derived from observations
  • separation P(a)dada/a between 2RRoche and
    200RRoche
  • eccentricity P(e)de 2ede
  • evolution of orbital parameters due to mass loss
    (stellar wind, mass transfert, supernova)
  • statistical properties
  • bNS 2.4 (systems that remain bounded after the
    second supernova)
  • P(t) 0.087/t (probability for a newly formed
    system to coalesce in a timescale t)
  • t0 2x105 yr (minimum coalescence time)

E gt 0
E gt 0
Vincent, 2002
7
The Galactic Coalescence Rate
8
Population Synthesis (fb)
  • single radio pulsar properties
  • Np 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)

Regimbau, 20012004
9
The Local Coalescence Rate
Bulk of stars formed in the first 1-2 Gyr. The
pairs merging today were formed with long
coalescence times (P (t) 1/t )
  • weighted average over
  • spiral (fS65) and elliptical (fE35) galaxies
  • same fb and bNS as for the Milky Way
  • spiral galaxy coalescence rate equal to the
    Milky Way rate
  • nS nMW (1.71)x10-5 yr-1
  • elliptical galaxy star formation efficiency and
    IMF estimated from observations - color
    metallicity indices (Idiart, Michard de Freitas
    Pacheco, 2003)
  • nE 8.6x10-5 yr-1
  • nc 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
10
The Detection Rate
  • coalescence rate within the volume V4/3 p D3
  • counts of galaxies from the LEDA catalog
  • - 106 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
  • maximum probed distance and mean expected rate
    (S/N7 false alarm rate1)

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 z6
  • numerical approach
  • generating extragalactic populations of NS/NS
    binaries

13
Extra slides
14
PSR J0737-3039 AB
.
.
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 Nobsi
  • Statistics
  • Nobsi follows a Poisson distribution of mean
    ltNobsgti
  • ltNobsgti ai Ntot
  • bayesian statistic to compute Pi(Ntot)
  • coalescence rate
  • Ri Ntoti/tlife fb
  • P(Ri) with mean and confidence level
  • combine P(Ri) to obtain P(R)
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