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The Parkes Pulsar Timing Array Project

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Title: The Parkes Pulsar Timing Array Project


1
The Parkes Pulsar Timing Array Project
R. N. Manchester
Australia Telescope National Facility, CSIRO
Sydney Australia
Summary
  • Project outline
  • Recent instrumental developments
  • Current results
  • Future prospects

2
The Parkes Pulsar Timing Array Project
Collaborators
  • Australia Telescope National Facility, CSIRO,
    Sydney
  • Dick Manchester, George Hobbs, David Champion,
    John Sarkissian, John Reynolds, Mike Kesteven,
    Warwick Wilson, Grant Hampson, Andrew Brown,
    Jonathan Khoo, (Russell Edwards, David Smith)
  • 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, Sam To
  • National Observatories of China, Beijing
  • Johnny Wen
  • Peking University, Beijing
  • Kejia Lee
  • Southwest University, Chongqing
  • Xiaopeng You
  • Curtin University, Perth

3
The PPTA Project Goals
  • To detect gravitational waves of astrophysical
    origin
  • To establish a pulsar-based timescale and to
    investigate irregularities in terrestrial
    timescales
  • To improve on the Solar System ephemeris used
    for barycentric correction

To achieve these goals we need weekly
observations of 20 MSPs over five - ten years
with TOA precisions of 100 ns for 10 pulsars
and lt 1 ?s for rest
  • Modelling and detection algorithms for GW
    signals
  • Measurement and correction for interstellar and
    Solar System propagation effects
  • Implementation of radio-frequency interference
    mitigation techniques

4
The PPTA Project
  • Using the Parkes 64-m radio telescope at three
    frequencies, 685 MHz, 1400 MHz and 3100 MHz, to
    observe 20 MSPs
  • Observations at 2 - 3 week intervals using
    10/50cm and 20cm receivers
  • Using polyphase digitial filterbanks and
    baseband recording systems
  • Regular observations commenced in mid-2004 using
    WBC, PDFB1 and CPSR2
  • New digital filterbank systems with higher time
    and frequency resolution PDFB2 commissioned in
    March 2007, PDFB3 in February 2008
  • New baseband recorder system (APSR) currently
    being commissioned
  • All data stored in PSRFITS format
  • mySQL database and processing pipeline -
    PSRCHIVE programs
  • Timing analysis - TEMPO2
  • GW simulations, detection algorithms and
    implications, galaxy evolution studies

5
Sky Distribution of Millisecond Pulsars
P lt 20 ms and not in globular clusters
6
New Observing Systems
CABB Processor Board
  • PDFB2, PDFB3 Digital Polyphase Filterbank
    systems
  • APSR Baseband recording system
  • Bandwidths 64, 128, 256, 512 or 1024 MHz
  • 8-bit digitisation of 2 or 4 inputs
  • On-line folding at pulsar period
  • 2048 channels x 2048 phase bins for 4-ms pulsar,
    more for longer periods
  • Up to 8192 channels or bins 4M max product
  • Real-time RFI rejection - adaptive FIR filters
  • Search mode - streamed data
  • Front-end for APSR system, 16 baseband chan.

PDFB3/APSR Block Diagram
7
PDFB3 - Initial Results
PSR B1641-45 (0.455 sec) 2048 bins x 2048
channels at 20cm 256 MHz bandwidth Raw spectrum
8
PDFB3 PSR J0437-4715 at 10cm
Pulse period 5.75 ms 1GHz bandwidth 2048 bins x
2048 channels
Raw Spectrum
Calibrated Spectrum
9
PDFB3 Search mode
  • 1-, 2-, 4- or 8-bit digitisation
  • 1, 2 or 4 polarisation products
  • 128 - 2048 channels
  • Sampling interval 32 ?s - 10 ms (Maximum rate
    dept on configuration)
  • Data files in PSRFITS format

Not yet fully commissioned
Vela at 1.4 GHz, 256 MHz bandwidth, 4-bit data
10
APSR Next Generation Baseband System
  • Swinburne/ATNF collaboration. Uses PDFB3 as a
    frontend.
  • 16 baseband channels over 64 - 1024 MHz
  • 8-bit digitisation for 64 - 256 MHz, 4-bit for
    512 MHz, 2-bit for 1024 MHz
  • 4 x 10 Gb ethernet to 16 dual-quad-core Dell
    processors
  • Quasi-real-time coherent dedispersion and
    folding
  • Web-based interface.

11
PDFB3 Real-time RFI Mitigation
System devised by Mike Kesteven, implemented by
Andrew Brown and Grant Hampson
  • Reference antenna pointed at RFI source
  • 2048 channels across band
  • Signalreference cross-correlation subtracted
    from data
  • Filter updates at 1ms intervals to follow
    tropospheric multi-path propagation
  • Single reference can be applied to both
    polarisations of telescope signal
  • Main application (so far) Digital TV signals in
    50cm band
  • 4-m reference antenna pointed toward Mt Ulandra,
    200 km south of Parkes

64 MHz at 50cm (653-617 MHz)
RFI Mitigation Off
Mt Ulandra TV signal
50cm Receiver
Cross-Correlation
12
PSR J0437-4715 at 50cm
RFI Mitigation On
Stokes I
S/N 1710!
RFI Mitigation Off
S/N 1040 in 4 min
  • Pulsar signal under RFI is recovered with no
    (evident) perturbation
  • Improvement in S/N will be greater with weaker
    pulsars
  • Expect to apply to regular 50cm observations
    with APSR soon

13
Pipeline Processing of PPTA data
  • Data transferred from Parkes to Epping over 1Gb
    ethernet, usually within a day or two of
    observations, stored on RAIDs
  • mySQL database used to keep track of data and
    processing status
  • PSRCHIVE programs used for data processing
  • PPTA1 script Automatic zapping of narrow-band
    and impulsive RFI
  • PPTA2 script Polarisation and bandpass
    calibration, scrunching in frequency time and
    polarisation, computation of TOAs using analytic
    profile templates, TEMPO2 residual plots.
  • Manual data checking and correction, flagging of
    unrecoverable data
  • PPTA3 script Computation and application of DM
    corrections to TOAs, recomputation of TEMPO2
    residual plots

System developed by George Hobbs, David Champion
and Xiaopeng You
14
Analytic Profile Templates (all 20cm)
PSR J0437-4715
PSR J17130747
PSR J1744-1134
PSR J18570943
15
Timing Residuals for PSR J0437-4715
  • PDFB2 at 10cm
  • 1 GHz bandwidth
  • 1.2 years data span
  • 64 min obs time
  • 211 TOAs
  • Weighted fit for 9 parameters ?, ?, F0, F1,
    Kepler binary parameters
  • No DM correction
  • Reduced ?2 2.87

Rms timing residual 56 ns!!
16
PPTA Pulsars One year of PDFB2 data
  • Timing data at 2 -3 week intervals at 10cm or
    20cm
  • TOAs from 64-min observations (except
    J18570943, J19392134, J2124-3358, each 32 min)
  • Uncorrected for DM variations
  • Solve for position, F0, F1, Kepler parameters if
    binary
  • Four pulsars with rms timing residuals lt 200 ns,
    eleven lt 1 ?s
  • Best results on J0437-4715 (56ns), J1909-3744
    (130 ns), J19392134 (150ns)

Best timing results yet!
17
DM Corrections
  • 10cm/20cm and 50cm CPSR2 data
  • About 4 yr data span
  • Routinely applied to all 20 pulsars

?DM of 10-3 corresponds to ?t 2.1 ?s at 20cm
18
Timing Residuals
  • PDFB1/PDFB2 data
  • 3-year data span
  • DM-corrected

10cm/20cm, reduced ?2 5.67
20cm, reduced ?2 1.40
Rms residuals roughly double 1-year PDFB2 results.
Still some systematic errors.
19
What next?
  • Investigate reasons for outliers and correct if
    possible
  • Correct for feed cross-coupling where necessary
    (MB data)
  • Develop and use frequency-dependant analytic
    templates
  • Systematic frequency dependence of TOAs across
    band commonly observed - can be as large as 2 ?s
  • Probably intrinsic profile variation, but may
    have instrumental component
  • Calibrate and remove instrumental delays
  • Pulse-modulated calibration signal - 1 ms
    periodicity
  • Analyse using standard TOA methods - can also
    check algorithms
  • Measurement precision a few nanoseconds
  • Avoid need for jumps between instruments
  • More observing!

20
Future Prospects
  • We are now approaching the level of TOA
    precision that is required to achieve the main
    goals of PTA projects
  • Good chance that detection of nanoHertz GW will
    be achieved with a further 5 - 10 years of data
    if current predictions are realistic
  • Major task is to eliminate all sources of
    systematic error - good progress, but not there
    yet
  • So far, intrinsic pulsar period irregularities
    are not a limiting factor
  • Progress toward all goals will be enhanced by
    international collaboration - more (precise) TOAs
    and more pulsars are better!
  • Current efforts will form the basis for detailed
    study of GW and GW sources by future instruments
    with higher sensitivity
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