Post on 18-Jan-2016
Sarah Burke Spolaor
Jet Propulsion Laboratory, California Institute of Technology
Gravitational Wave Detection with Pulsar Timing Arrays:Status and Prospects
© 2013 California Institute of Technology, Government Sponsorship Acknowledged
Millisecond pulsars
Spinning up to ~700 times per
second
“Timing Residuals”Model pulsar Observe Correct?
Mod
el
– A
ctu
al
Arr
ival
Ph
ase
(m
s)
Time (relative MJD)
Figure of Merit: RMS scatter of
residuals.
BEST: <50nsWORST: few ms
Fit for known effects
Example pulsar modelP
SR
J0437-4
715
Also referenced:
• JPL Planetary ephemeris
• TAI international atomic time standard
Pulsar
Earth
Jenet et al. (2004)
Pulsar Timing Array
• Monopolar signature?• Atomic time standards (Hobbs et
al. 2012)• Telescope issues
• Dipolar signature?• Planetary ephemeris errors
(Champion et al. 2010)
• Quadrupolar signature?• Gravitational waves
GW SPECTRAL BAND:Observing cadence Experiment length
~2 weeks to >10 yearsnHz – mHz
GW Spectrum
Adapted from Yardley et al. (2009)
log
[d
imen
sion
less
GW
str
ain
]
Stochastic SMBH Binary Background
UNTIL RECENTLY:“Working on our sensitivity”
CURRENTLY & UPCOMING: Meaningful upper limits
+Detection
GW BackgroundN
orm
ali
zed
Dis
trib
uti
on
Strain Amplitude at f = (1 year)-1
ALL MODELS
Fiducial models
Low-mass BCG
High-mass BCG
Adapted from Sesana et al (2013)
GW Background
Van Haasteren et al. 2013
Shannon et al. (accepted to
Science)
Norm
ali
zed
Dis
trib
uti
on
Strain Amplitude at f = (1 year)-1
ALL MODELS
Fiducial models
Low-mass BCG
High-mass BCG
Rules out standard Millennium Simulation
binary presecription to 50% confidence
Sensitivity scaling law
S/N
Number of pulsars
Average residual RMS Number of observations
Length of experiment
Scaling law from Siemens et al. (2013)
b = 13/3 for SMBH binary background
Recent Sensitivity Improvements:
Gaussian & Non-stationary Noise
Recent Sensitivity Improvements: Detection
Algorithms• Coherently seek correlations using all pulsars
• More sensitive statistical analysis
• Resolved sources:
• Corbin+Cornish10; Finn+Lommen+10; Lee+11; Ellis+12; Boyle+Pen12; Mingarelli+12; Ellis13 …
• Sky localization (~2000 deg2; Ellis 2013)
• Parameter estimation (M, e, D, P …)
• Measuring Spin-orbit Precession
Recent Sensitivity Improvements: Detection
Algorithms
Incoherent spectral analysis
(Yardley+09)
Bayesian inference(Ellis et al. in prep)
Thanks to J. Ellis for figure
Yardley et al. (2009) data set: two algorithms
Recent Sensitivity Improvements: Detection
Algorithms• Coherently seek correlations using all pulsars
• More sensitive statistical analysis
• GW Backgrounds:
• van Haasteren+11; Demorest+12; Shannon et al (accepted)
• IPTA data challenge (12 distinct submissions, paper in prep)
Recent Sensitivity Improvements:
International Pulsar Timing Array
• Nanohertz Observatory for Gravitational Waves (NANOGrav; North America)
• European Pulsar Timing Array (Europe)
• Parkes Pulsar Timing Array (Australia)
http://www.ipta4gw.org
Recent Sensitivity Improvements:
International Pulsar Timing Array
• DOUBLE number of pulsars [~40 total]
• LONGER data sets [up to 30 years]
• LOWEST RMS RESIDUALS pulsars [many under 500ns]
• LARGE NUMBER OF DATA POINTS
S/N
Number of pulsars
Average residual RMS Number of observations
Length of experiment
Scaling law from Siemens et al. (2013)
b = 13/3 for SMBH binary background
100 Pulsars10 yr per pulsarCoherentOptimistic timing precision
The Future:Resolved SMBH Binaries
z = 0.001
z = 0.01
z = 0.1
Optimistic Future timing array
with Square Kilometre Array
Burke-Spolaor (2013; CQG Special issue on Pulsar Timing Arrays)
Confusion limit?(Boyle & Pen 2012)
2e9Msun atInternational Timing Array 2014
+ Ellis+12 Bayesian algorithm
Yardley et al. (2010)
The Future: GW Background
Shannon et al. (submitted)
Square Kilometre Array100 pulsars, RMS < 100ns,
for 10 years
Norm
ali
zed
Dis
trib
uti
on
Strain Amplitude at f = (1 year)-1
ALL MODELS
Fiducial models
Low-mass BCG
High-mass BCG
IPTA est.
The Future: GW Background
With three new
pulsar discoveri
es per year
Continuing without improvem
ent
Only NANOGrav considered here (Siemens et al. 2013)
Summary• Galactic-scale gravitational wave observatory
• Supermassive black hole binaries anticipated first detection: Individual/Stochastic Background
• Gravitational waves in ~9 years WITHOUT improvements.• IPTA formation• Enhanced algorithms and more pulsars• Improved instrumentation + understanding of
“detector” (pulsar)
• Timing Array science not covered:• Multi-messenger targets• Strongest observational limits on cosmic string tension• Testing alternate theories of gravity• Detecting trans-Neptunian objects• Spacecraft naviation with timing arrays
Grab-bag:Alternative gravity
theoriesLee+08
Where to look?Burke-Spolaor (2013; CQG Special issue)
References: Comerford+09, Liu+10, Shen+11, Komossa+03, Fabbiano+11, Graham04, Milosavljevic+Phinney05, Sesana+11, Tanaka+12, Eracleous+11, Burke-Spolaor11, Gower82, Volonteri+08, and more
Red: not yet confirmed
Grab-bag: Astrophysics with GW
limits• 3C66B (Sudou+03, Jenet+04)
• 1.06 year orbit (Pgw = ½ year)
• Total mass > 1010 Msun
Simulated 3C66B signal… Actually saw…