pulsar stability - australia telescope national facility · pulsar stability (and) outline • high...
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Joris Verbiest Swinburne University & ATNF
Matthew Bailes (Swin) Richard Manchester (ATNF)
George Hobbs (ATNF) William Coles (UCSD) Andrea Lommen (F&M)
*: GWB = Gravitational Wave Background
Pulsar Stability (and
)
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Outline
• High precision timing of MSPs*
• Long-term timing stability
• Simple GWB limit technique
• Conclusions
*: MSP = Milli-Second Pulsar
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Quick Basics of Pulsar Timing
Time (10 years)
Res
idua
l (20
0 ns
)
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Precision Timing State-of-the-Art
• PSR J0437-4715
• 10 years
• 4 instruments
• 200 ns rms
• Highest precision over decade! (Verbiest et al., 2008)
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Long-term Stability of MSPs
GWB sensitivity requires: (Jenet et al., 2005) – High timing precision ( ~102 ns)
– Long observing campaigns (~101 yrs)
⇒ Highly stable MSPs
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Expected GWB signature
LOW frequency
LOW strain (strength)
(Fig
ure
cour
tesy
of G
. Hob
bs)
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Stability: Observations
• 12 years (avg.) on 20 PPTA* pulsars
*: PPTA = Parkes Pulsar Timing Array
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Stability: Examples: 1824 PSR J1824-2452 (in Globular Cluster M28)
Time →
Resi
dual
(low) Frequency (high)
Pow
er
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Stability: Examples: 1909 PSR J1909-3744:
158 ns over 5 yrs
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Stability: Observations
• 12 years (avg.) on 20 PPTA* pulsars – 2: clear timing noise (J1939+2134, J1824-2452) – 2: some evidence for timing noise (J0613-0200, J1024-0719)
– 4: sub-μs timing (J0437-4715, J1909-3744, J1713+0747, J1744-1134)
– 12 remaining: white noise, μs-level rms
– average: 2.2 μs rms
*: PPTA = Parkes Pulsar Timing Array
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Stability: Conclusion & Prospects
• Mostly stable, but high noise levels
• New instruments (bandwidth, resolution) • New calibration methods • New software • New pulsars (surveys) • Collaboration (more, bigger telescopes)
Detection prospects look good, provided:
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PTAs need to “see” the GWs True Residuals
True Residuals + simulated GWB
Simulated GWB
PSR J1939+2134 PSR J1857+0943 PSR J0437-4715
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GWB vs. Pulsar Spectrum
GWB
PSR J0437-4715
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A Very Simple GWB Limit • Spectrum of Pulsar Residuals: PPSR(f)
• Monte-Carlo GWB Spectrum: PGWB(A,f)
• Statistic: S = Σ( W(f) * P(f) )
• Bound: amplitude for which SGWB > SPSR , 95% of the time
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Previous Limits in Literature
• Kaspi, Taylor & Ryba, ApJ, 1994
• Thorsett & Dewey, Ph. Rev. D, 1996
• McHugh et al., Ph. Rev. D, 1996
• Jenet et al., ApJ, 2006
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Earlier Limit Problems • No GWB simulations - all analytic
– Fitting, jumps & sampling effects – Hard Statistics
• White residuals required (Jenet et al., 2006)
• GWB simulation software ( Hobbs et al., 2008)
– Monte-Carlo simulations • Red noise allowed
Then
Now
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Details to be Worked Out
• Precise weighting (i.e. combination of frequencies)
• Combination of Pulsars
• Spectral leakage
• Steep spectra
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No (New) Limit
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Conclusions
• MSPs are intrinsically stable
• Limits are useful too
• Promising new limit coming soon
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Gravitational Wave Effect
Source: Wikipedia
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Results (Summary)
GC
Timing Noise
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GWB vs. Pulsar Spectrum
GWB
PSR J0437-4715
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Stability: Examples: 1713 PSR J1713+0747:
362 ns over 14 yrs