Low Frequency Observations of the ISM and Pulsar Timing

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Low Frequency Observations of the ISM and Pulsar
Timing

• Joris Verbiest

Swinburne University ATNF, Australia
Xiaopeng You (Southwest University,
China) William Coles (UCSD) George Hobbs (ATNF)
PPTA team
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Outline

• Brief intro to PPTA
• DM variations and the turbulent ISM
• PSR J0437-4715s DM Structure Function
• TOA-intensity correlation
• Summary

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PPTA Team Members

• Australia Telescope National Facility, CSIRO,
  Sydney
• Dick Manchester, George Hobbs, David Champion,
  John Sarkissian, John Reynolds, Mike Kesteven,
  Warwick Wilson, Grant Hampson, Andrew Brown,
  David Smith, Jonathan Khoo, (Russell Edwards)
• Swinburne University of Technology, Melbourne
• Matthew Bailes, Willem van Straten, Joris
  Verbiest, Ramesh Bhat, Sarah Burke, Andrew
  Jameson
• University of Texas, Brownsville
• Rick Jenet
• University of California, San Diego
• Bill Coles
• Franklin Marshall College, Lancaster PA
• Andrea Lommen
• University of Sydney, Sydney
• Daniel Yardley
• National Observatories of China, Beijing
• Johnny Wen
• Peking University, Beijing
• Kejia Lee
• Southwest University, Chongqing
• Xiaopeng You
• Curtin University, Perth

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Pulsar Timing Arrays

• Main goal Detect gravitational waves
• Secondary goals Investigate time
  standards Investigate Solar System Investigate
  ISM

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DM Variations in Timing
50cm 20cm
10cm 20cm
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PPTA DM Variations

• You et al., MNRAS, 2007

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DM Structure Function

• Measure of turbulent power at different scales
• Expected to be exponential with spectral index
  a 5/3 for Kolmogorov model

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Typical SF
You et al., MNRAS, 2007
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Kolmogorov Slope
You et al., MNRAS, 2007
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Large Inner Scale
You et al., MNRAS, 2007
(10 days 0.4 AU)
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PSR J0437-4715 SF
You et al., MNRAS, 2007
1000 days 61 AU
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0437 DM Variations
500 days 30 AU
2004
2008
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Scintillation TOAs

• PSR J0437-4715
• 685 MHz
• 2 hours, 8sec integrations

TOA residual
Signal-to-Noise-1
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Scintillation/TOA - Simulations
Coles et al., in preparation
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Grad DM - Simulations
Coles et al., in preparation
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Correlation - Real Data
Coles et al., in preparation
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Conclusions

• PTAs need high timing precision.
• ? ISM effects need to be corrected
• ? Most easily measured at low frequencies
• ? ISM an interesting place that keeps surprising