Low Frequency Observations of the ISM

and Pulsar Timing

Joris Verbiest

Xiaopeng You (Southwest University, China)

William Coles (UCSD)

George Hobbs (ATNF)

PPTA team

Swinburne University & ATNF, Australia

Outline

• Brief intro to PPTA

• DM variations

and the turbulent ISM

• PSR J0437-4715’s

DM Structure Function

• TOA-intensity correlation

• Summary

Australia Telescope National Facility, CSIRO, SydneyDick 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, MelbourneMatthew Bailes, Willem van Straten, Joris Verbiest, Ramesh Bhat, Sarah Burke, Andrew Jameson

University of Texas, BrownsvilleRick Jenet

University of California, San DiegoBill Coles

Franklin & Marshall College, Lancaster PAAndrea Lommen

University of Sydney, SydneyDaniel Yardley

National Observatories of China, BeijingJohnny Wen

Peking University, BeijingKejia Lee

Southwest University, ChongqingXiaopeng You

Curtin University, PerthAidan Hotan

PPTA Team Members

Pulsar Timing Arrays

• Main goal: Detect gravitational waves

• Secondary goals:Investigate time standardsInvestigate Solar SystemInvestigate ISM…

DM Variations in Timing

50cm

20cm

10cm

20cm

PPTA DM VariationsYou et al.,

MNRAS, 2007

DM Structure Function

• Measure of turbulent power at different scales

• Expected to be exponential with spectral index α = 5/3 for Kolmogorov model

Typical SF

You

et

al.,

MN

RA

S,

20

07

Kolmogorov Slope

(1000 days ≈ 7.8 AU) You

et

al.,

MN

RA

S,

200

7

Large Inner Scale

(10 days ≈ 0.4 AU) You

et

al.,

MN

RA

S,

20

07

PSR J0437-4715 SF

1000 days ≈ 61 AU

You et al., MNRAS, 2007

0437 DM Variations

~500 days ≈ 30 AU

2004 2008

Scintillation & TOAs• PSR J0437-4715

• 685 MHz

• 2 hours, 8sec integrations

TOA residual Signal-to-Noise-1

Scintillation/TOA - Simulations

Cole

s et

al.,

in p

repara

tion

Grad DM - Simulations

Coles et al., in preparation

Correlation - Real Data

Cole

s et

al.,

in p

repara

tion

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…