Galactic Merger Rate of DNS Systems and Prospects for Detecting Gravitational Waves Chunglee Kim Nor

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Galactic Merger Rate of DNS Systems andProspects
for Detecting Gravitational WavesChunglee Kim
(Northwestern)

• with
• Vicky Kalogera (NU), Duncan R. Lorimer
  (Manchester),
• Richard OShaughnessy (NU) Chris Belczynski
  (New Mexico State)
• 7th Pacific Rim Conference
• Sejong Univ. Seoul (Nov. 3, 2005)

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• Global network of GW detectors

Based on interferometry
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• Double Neutron Star (DNS) Systems

? Before 2005, 7 systems are known in our
Galaxy. (discovered by radio pulsar surveys)

• ? 3 systems will merge within a Hubble time.
• (PSR B191316, B153412, and J0737-3039)

PSR J0737-3039 (Burgay et al. 2003) the 3rd
merging DNS the 1st double-pulsar system
extremely relativistic! merging timescale 85 Myr
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• Double Neutron Star (DNS) Systems

? Strong sources of gravitational waves
(waveforms are well understood)
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• How to calculate the DNS merger rate?

? Theoretical method based on our
understanding of binary formation and
evolution (population synthesis models)
(Portegies Zwart Yungelson (1998), Nelemans et
al. (2001), Belczynski, Kalogera, Bulik
(2002), and many more) ? Empirical method
based on radio pulsar properties and
observational selection effects of pulsar
surveys (Narayan et al. (1991), Phinney
(1991), Curran Lorimer (1993), Kalogera
et al. (2001), Kim et al. (2003))
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• Merger rate R

Q) How many of pulsars similar to each of known
DNS systems exist in our Galaxy?
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Goal Calculate the probability distribution of
the Galactic DNS merger rates P(R) !
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• Method - Modeling Simulation (Kim et al. 2003,
  ApJ, 584, 985 )

1. Model pulsar sub-populations
Selection effects for faint pulsars are taken
into account.
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• Method - Modeling Simulation (Kim et al. 2003,
  ApJ, 584, 985 )

2. Simulate large-scale pulsar surveys
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• Statistical Analysis

? Apply Bayes theorem to calculate P()
P() ? P(Nobs ) where P(Nobs
) is obtained from the simulation
Use the relations,
(fb)
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• Statistical Analysis

? Individual probability density function (PDF)
For an each observed system i, Pi(R) Ci2R
exp(-CiR) where Ci
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P(Rgal)

• ? Double neutron star (DNS) systems
• 3 merging systems in the Galactic disk
• (PSR B191316, B153412, and J0737-3039)

ground-based GW detectors
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• Probability density function of Rgal

Lifetime 185 Myr (shortest) NJ0737 1600 (most
abundant)
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• Probability density function of Rgal

Rpeak
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• The revised DNS merger rate

due to the discovery of PSR J0737-3039
? Reference model
B1913B1534J0737
B1913B1534
merger rate
Rgal (revised) (Myr-1)
Rgal (previous) (Myr-1)
(at 95 CL)
209
83
13
-66
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• Detection rate of DNS inspirals for LIGO

due to the discovery of PSR J0737-3039
? The most probable DNS inspiral detection rates
for LIGO
Reference model
All models
Rdet (ini. LIGO) 1 event per 10 400 yr
Rdet (adv. LIGO) 10 500 events per yr
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• Global P(Rgal) motivation

? Radio pulsar luminosity function
f(L) ? L-p, where Lmin is a cut-off luminosity
and p is a power index.
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• Global P(Rgal) motivation

? 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)
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• Global P(Rgal) and SNe rate constraints

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• Global P(Rgal) and SNe rate constraints

Conservative upperlimit of Rgal
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• Implications of J1756-2251

? J1756-2251 The newly discovered merging DNS
in the Galactic disk
(Faulkner et al. 2005)
? discovered by the Parkes Multibeam Pulsar
Survey with the acceleration search
technique. Standard Fourier techniques
failed to detect J1756-2251.
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• Summary

J0737-3039 and DNS merger rate DNS merge events
are more frequent than previously thought !
Rgal,peak 4 - 220 per Myr increase rate
factor 6 - 7
Detection rates for DNS inspirals

• Rdet (ini. LIGO) 1 event per 10 400 yr
• Rdet (adv. LIGO) 10 500 events per yr

Empirical SNe rates and the upper limit of
Rgal SNe rates provide stringent constraints on
the DNS merger rate, but a quantitative study is
difficult.
and J1756-2251 Similar to the Hulse-Taylor
pulsar. No significant change in Rgal