Implications of PSR J0737-3039B for
the Galactic NS-NS Binary Merger Rate
Chunglee Kim (Yonsei University)
with Ben Perara and Maura McLaughlin
Amaldi2015, Gwangju
[Image: NASA]
stellar-mass Compact Binary Coalescences (CBCs)
Global network of GW detectors
[Image: NASA]
stellar-mass Compact Binary Coalescences (CBCs)
O(10-1000) Hz frequency band “on Earth”,
stellar-mass binaries
Global network of GW detectors
One of the best example of CBCs for Earth-bound detectors:
Neutron star - neutron star (NS-NS) binary mergers
a typical pulsar-NS binary
companion
neutron star
recycled (first-born NS)
or non-recycled (second-born NS)
radio pulsar
“All known NS-NS binaries are PSR-NS binaries”
There are 4 confirmed pulsar-NS binary mergers in the Milky Way disc.
One of them consists of two radio pulsars:
The Double Pulsar!
The Double Pulsar PSR J0737-3039
first-born NS
old, recycled,
millisecond pulsar
second-born NS
young, non-recycled,
slowly-rotating pulsar
PSR J0737-3039A
or A pulsar
PSR J0737-3039B
or B pulsar
Burgay et al. (2003)
pulsar
name
spin
period
(ms)
period derivative
(10-18 ss-1)
Lyne et al. (2004)
mass
characteristic
age (Myr)
140
50-190
binary merger
timescale (Myr)
85
radio emission
timescale (Myr)
> Hubble time
Observed and estimated properties of the PSR J0737-3039A and B pulsars.
Two pulsars, one binary merger
40
Current understanding of pulsar binaries as GW sources
Q: Do we understand properties of merging PSR-NS binaries? more or less
(i.e. formation/evolution channels/distribution in the Milky Way)
Q: Are they detectable ?
Y
Q: Do we have a good waveform model?
Y
Q: What is a source event rate (PSR-NS coalescences)?
1-100 per Myr
−1
Rg ∼ 21+28
Myr
−14
Q: How many of such events can be detectable by GW detectors?
at least 1 detection per year or
1 detection in monthly basis
−1
Rdet = 8+10
yr
−5
Galactic NS-NS merger rate estimates until 2010
Based on recycled pulsars in known PSR-NS binaries in the Galactic disk
The beaming fraction of the A pulsar was assumed to be similar to
those measured from PSRs B1913+16 and B1534+12
(~ 17 % beaming fraction or a beaming correction factor of 6).
Kalogera, CK, et al. (2004)
Galactic NS-NS
merger rate (empirical)
The LSC-Virgo “rates” paper (Abadie et al. 2010)
GW detection rate estimates extrapolated
from Galactic NS-NS merger rate
Pulse profile evolution of the B pulsar
2003
S/N
=228
2008
S/N
=11
perera et al. (2012)
The B pulsar is more difficult to detect than the A pulsar
We consider binaries consisting of
A-like AND B-like pulsars, classifying
as a population like PSR J0737-3039
in the Milky WAy disc.
N_observables x correction factors
= true population size Npop
There are many binaries consisting of A-like
pulsars with “dead” B pulsars (after B’s radio
emission is halted). These are not included
in our simulation.
B is observable only
~50% of its orbital phase
We do account for different detectabilities for
A and B pulsars, in order to calculate
the true population size Npop
weak phases
1 and 2
bright phases
1 and 2
weak phases
1 and 2
• We expect there are total 500 - 6000
Double Pusar-like binaries in the disk (95%)
Lyne et al. (2004)
We understand A and B beam geometries better than 2004!
A pulsar
polarization measurements
B pulsar
pulse profile analysis
(Demorest et al. 2004)
(Perera et al. 2010, 2012, and this work)
pulse profile analysis
polarization measurments are difficult, due to
strong modulations in the pulse profile induced by
geodetic precession
(Ferdman et al. 2008, 2013;
Perera, CK et al. 2014)
�fb,eff,A � ∼ 2
α ∼ 90◦ +5
−10 orthogonal rotator
ρ ∼ 11◦ − 18◦ or ∼ 30◦
�fb,eff,B � ∼ 3 − 4
α = 61◦ (best − fit)
ρ = [5◦. 5, 14◦. 3]
It was possible to include the B pulsar in rate calculation only after Perera et al.
published pulse profile analysis results of the B pulsar,
using the 5-yr data obtained from the Green Bank Telescope.
This work
• Estimating beaming correction factors for B, for the first time,
using the beam geometry obtained from latest pulse profile analyses
• Including the B pulsar in the rate calculation
•Using 4 pulsars (in 3 PSR-NS binaries) with best observational constraints:
PSRs B1913+16, B1534+12, J0737-3039A, and J0737-3039B
(CK, Perera, & McLaughlin, 2015)
We constrain the B pulsar’s beam geometry by fitting its pulse profile
that evolves over the 5-yr observations the Green Bank radio telescope
NS-NS merger rate
in the Milky Way
=
number of pulsar-NS mergers similar to those observed N
effective liftime of such binary mergers
• Rate calculation: Monte Carlo simulations to compute p(N| 1 detection)
model assumptions (x,y,z,L)
lifetime is estimated from pulsar observations
• Main uncertainty: pulsars’ beam geometry (or the beaming fraction),
“age” of the binary since the 2nd NS has been formed
and Galactic pulsar luminosity function
cf) “rate” estimation is not sensitive to Galactic pulsar distribution,
unless the bulge population is highly underestimated (see Kim, Kalogera, Lorimer 2003)
step 1. Calculate individual PDFs of NS-NS merger rate,
PA(R) and PB(R) for the A and B pulsars, respective
Use observed properties of A and B to calculate NA and NB
Use the “effective” lifetime of the Double Pulsar as a common parameter
(We use A’s spin-down age + B’s radio emission timescale)
step 2. Combining PA(R) and PB(R) to calculate
P(R) for the Double Pulsar
Assume detecting A or B pulsar is an independent process
likelihood of detecting
the Double Pulsar
(both A and B)
= likelihood of detecting A (with B as its companion)
x
likelihood of detecting B (with A as its companion)
Result 1: How many Double Pulsar-like binariese are in our Galactic disk?
solid: Double Pulsar
dotted: A only
dashed: B only
• If we correct selection biases perfectly,
total estimated number of psrs like A
~ # of psrs like B
~ # of systems like the Double Pulsar
~ 1500 (most likely from the combined PDF)
Result 2: Galactic PSR-NS merger rate and the inferred GW event rate
NS-NS merger rate
dotted: B1913+16
short-dashed: J0737-3039
solid: all (1913+1534+0737)
−1
Rg ∼ 21+28
Myr
−14
Galactic NS-NS merger rate is
NOT dominated by
a single system.
GW detection rate
−1
Rdet = 8+10
yr
−5
95% confidence interval
Comments on PSR J1906+0746
van Leeuwen et al. (2015)
The companion of J1906+0746 is heavier than the pulsar.
Is it a cousin of PSR J0737-3039, where only the non-recycled pulsar is detectable?
Or is it an NS - (heavy, old) WD binary went through an exotic mass transfer history?
Ps (ms)
Porb (days)
e
pulsar mass
(Msun)
companion mass
(Msun)
1.291(11)
1.322(11)
companion
type
NS? or heavy WD?
If we assume Npsr~200 (from our simulation), beaming correction factor of 3.4
(empirical spin-opening angle relation), radio-observable lifetime of 80 Myr,
the Galactic NS-NS merger rate can be increase by a factor of 2
by including PSR J1906+0746
Our results are consistent with sGRB rate and theoretical expectations
but we can do better with GW detections
coward et al. (2012)
detection rate based on 340 Mpc
Belczynski et al. (2008)
our work
our work
∼ 10Gpc−3 yr−1
based on 8 Swift sGRBs with z measurements
(popsyn) NS-NS merger rate : ~ 1 - 100 Myr-1
(empirical) NS-NS merger rate : ~ 3 - 20 Myr-1
150-2000 Gpc-3 yr-1 [Gehrels]
(if all sGRBs are formed from NS-NS mergers, beaming angle ~ 5-20 deg)
At 99% C.L., the NS-NS merger rate per volumn from our work is
Rgal,NS−NS ∼ 50 − 700 Gpc−3 yr−1
Summary
• We calculate observational biases for PSR J0737-3039B by detailed pulse profile
analysis using the 5-yr GBT data
• We calculate the Galactic NS-NS merger rate using observed properties of PSRs
B1913+16, B1534+12, and the Double Pulsar (based on A and B pulsars)
• We expect 1 GW detection per year (pessimistically) or 1 detection in monthly
basis (optimistically), regarding NS-NS coalescences for the 2nd generation GW
detector network
• Model uncertainties in Galactic pulsar population can be constrained with GW
detections!
Galactic NS-NS merger rate
−1
Rg ∼ 21+28
Myr
−14
GW detection rate
−1
Rdet = 8+10
yr
−5
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http://arxiv.org/pdf/1308.4676v3.pdf
Figures 4 and 5 were swapped in v2 and in the manuscript published in MNRAS.
Figure orders are corrected in v3. Captions are all correct. No change in the text