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Pulsar Timing and Galaxy Evolution
Common Ground in the GWB
Sarah Burke
Swinburne University/ATNF
ATNF GW Mtg
December 12, 2008
Supervisors:
Matthew Bailes,
David Barnes,
Simon Johnston,
Dick Manchester
In collaboration with:
Dick Manchester,
Ron Ekers,
Chris Phillips
CLAIM
Pulsar timing should detect GW emission
from binary supermassive black hole
(SMBH) systems at sub-pc separations
Supermassive: mBH > ~106 MSun
GW detection from PTing
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GWB
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A background of emission
from hard binaries
Supermassive systems
with BH mass ratio >0.3
Porb = 106 - 108 s
Contributing population
anywhere from z = 0 to
high redshift (z > 6)
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Single source
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Nearby (z<1)
Porb = 106 - 109 s
Very close orbital
separation;
a < ~0.1 pc
All binary black holes must have been formed via a
galaxy merger and undergo subsequent inspiral
processes before reaching the pulsar regime.
The modelling approach
1.
How many merged galaxies exist?
- How many galaxies containing SMBHs are merging?
- What is the BH mass function?
- When/where in the universe did the merger happen?
2.
What is the timescale for inspiral,
coalescence of a resulting SMBH
binary?
Characteristic Strain
Stochastic GWB Sources
Gravitational wave frequency
A long way to go!
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“Last parsec” problem is still unresolved!
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Binary SMBH populations unknown
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Even at earlier stages of binary evolution
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Hierarchical models vs. Monolithic
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No local binary black holes to test GR theory
and pulsar timing methods.
CLAIM
Identification of SMBH binary systems in
local galaxies will be beneficial to pulsar
timers and galaxy evolutionists
Thus far, all binary evidence has been tenuous
and (nearly) all claims for binaries have been
indirect
Binary Detection Methods
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cetera
A robust, direct binary BH
detection method
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Exploitation:
 Unique
spectral energy distribution of AGN
 Relation of AGN to BHs (Ron’s talk)
 Existence of double, compact flat/inverted
spectrum sources not yet explored
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Combined with:
 High-frequency
selection favours AGN
(AT20G)
 Good LBA resolution (~1 mas)
log amplitude
0402+379
Rodriguez et al. 2006
Double
nucleus
log amplitude
log frequency
Direct Detection:
Spatially Resolved Systems
log frequency
Parameter space
2-point
correlations
Number
CLASS
Galaxy merger
rates
VLBI
Pulsar timing
sensitivity
AT20G
Chance radio, xray double detections
0 1 10 100 1000 1e4 1e5 1e6 1e7 1e8 --->
Integrated over redshift
bin and BH mass range
Linear separation between most
massive galactic BHs (pc)
Parameter space
Number
Galaxy groups,
large scale
clustering, chance
projeted separations
Bound binary
BH systems
0 1 10 100 1000 1e4 1e5 1e6 1e7 1e8 --->
Integrated over redshift
bin and BH mass range
Linear separation between most
massive galactic BHs (pc)
Where things get interesting
Number
3-body interactions
with stellar
background
GW emission;
final inspiral
Binary
hardening
Jaffe and Backer
(2003):
N  a13/2
0 1e-3 1e-2 0.1 1 10 100 1000 1e4 1e5
BH separation
Where things get interesting
Number
Hard binary stage:
longer than a
Hubble time?
DANGER!
NO astrophysical
Efficient loss-cone
gravitational wave
repopulation
background!
Stall
region?
0 1e-3 1e-2 0.1 1 10 100 1000 1e4 1e5
BH separation
Aiming for results
LBA resolution limit
VIPS resolution limit
Sources in a GW regime
that will coalesce in
t = 1/H0 (H0 = 72 km/s/Mpc)
Preliminary Counts
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CLASS
 Imaging
and spectral indices of ~10000 flatspectrum sources
 149 sources with multiple flat-spectrum
components identified
 22 identified as gravitational lenses
Preliminary Counts
Short-long baseline
Visibility ratio
Australia Telescope 20GHz Survey
Blue: spectral index -0.5
Yellow: spectral index -0.3
Rajan Chettri,
Ron Ekers
Preliminary Counts
At the moment…
a little bleak
10
30
50
70
N
90
110
130
CLASS
0402+379
NGC6240
0 1e-3 1e-2 0.1 1 10 100 1000 1e4 1e5
BH separation
Science aims

Pulsar timing:
 Possible
discovery of individual GW-emitting
sources
 Observationally constrained
parameters/scenarios in GWB models
 Stochastic GWB power spectrum based on
actual sources or predictions from counts
 With any detections, can put a lower limit on
the GWB for pulsar timing.
 Direct evidence for close binary black holes
and black hole coalescence
Science aims
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Merger dynamics & MBH Evolution:
 Observational
check of hierarchical galaxy
formation models
 Local binary population count
 Discovering new BH systems: ability to study
host galaxies and post-merger dynamics,
timescales.
(END)
Outline of talk
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1. The problem & background
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2. How we’re approaching
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Pulsars detect binaries in a unique frequency range
Binary populations unknown
GWB models are very unconstrained
Galaxy evolution models are very unconstrained
CUT TO THE CHASE:
Direct observations of BHs are possible!
And will give science. Show N vs a plots, or some a/adot
vs a plots.
3. What will result

No detections: various interpretations; BHBs do not
exist, or only exist only for very short periods of time.
 An OBSERVED lower limit for a GWB (statistical or
actual)