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Pulsar timing with tempo2

Pulsar timing with tempo2. George Hobbs Australia Telescope National Facility george.hobbs@csiro.au. Contents. Basis of pulsar timing Getting tempo2 Using tempo2 Developing tempo2. Must average many thousands of pulses together to obtain stable profile.

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Pulsar timing with tempo2

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  1. Pulsar timing with tempo2 George Hobbs Australia Telescope National Facility george.hobbs@csiro.au

  2. Contents • Basis of pulsar timing • Getting tempo2 • Using tempo2 • Developing tempo2 CSIRO. Gravitational wave detection

  3. Must average many thousands of pulses together to obtain stable profile Must convert to conform with terrestrial time standards Must convert to reference frame suitable for the timing model – e.g. solar system barycentre Must convert to arrival times at infinite frequency Must add extra propagation delays e.g. through the solar system Pulsar timing: The basics(see Hobbs, Edwards & Manchester 2006, MNRAS) Model for pulsar spin down Improve timing model Obtain pulse arrival times at observatory Form timing residuals – how good is the timing model at predicting the arrival times CSIRO. Gravitational wave detection

  4. Tempo2 • Paper 1: Hobbs, Edwards & Manchester (2006), MNRAS, 369, 655 • Paper 2: Edwards, Hobbs & Manchester (2006), MNRAS, 372, 1549 • Paper 3: Hobbs, Jenet, Lee et al. (2009), MNRAS, 394, 1945 CSIRO. Gravitational wave detection

  5. Getting tempo2 • Wiki: http://www.atnf.csiro.au/research/pulsar/tempo2 • Main repository: https://sourceforge.net/projects/tempo2/ • Get data: • >cvs -z3 -d:pserver:anonymous@tempo2.cvs.sourceforge.net:/cvsroot/tempo2 co tempo2 • Email distribution list: http://lists.pulsarastronomy.net/mailman/listinfo/tempo2_lists.pulsarastronomy.net • Ingrid’s help page for using tempo2: http://www.astro.ubc.ca/people/stairs/tempo2.html CSIRO. Gravitational wave detection

  6. Paper I: overview • Tempo2 accurate for known physics to 1ns (factor of ~100 better than tempo1 and ~1000 better than psrtime) • Tempo2 is compliant with the general relativistic framework of the IAU 1991 and 2000 resolutions - uses the international celestial reference system, barycentric coordinate time and up-to-date precession, nutation and polar motion models CSIRO. Gravitational wave detection

  7. Paper I: overview • Two parts to tempo2: 1) Forming the pulse emission time and 2) updating the pulsar timing model • 1) Forming the pulse emission time Secular motion SS Shapiro delay Solar system Einstein delay Dispersive component Orbital motion Clock corrections SS Roemer delay Atmospheric delays CSIRO. Gravitational wave detection

  8. Forming the pulse emission time: clock corrections • TOAs are recorded against local observatory clocks • Probably don’t have good long term stability • Can transform to the best terrestrial time-scale by applying corrections derived from monitoring the offsets between pairs of clocks • E.g. Parkes clock -> GPS -> UTC(AUS) -> UTC -> TAI • UTC = time-scale formed through the weighting of data from an ensemble of atomic clocks • TAI = UTC + leap seconds to maintain synchrony with Earth’s rotation CSIRO. Gravitational wave detection

  9. Clock corrections • Clock corrections are in > $TEMPO2/clock Part of pks2gps.clk CSIRO. Gravitational wave detection

  10. Atmospheric propagation delays • Can get effects by the ionised fraction of the atmosphere (ionosphere) and the neutron fraction (mainly the troposphere). It is possible to provide TEMPO2 with lists of surface atmospheric pressure for the most accurate determinations. • Not normally needed! CSIRO. Gravitational wave detection

  11. Einstein delay • Damour & Deruelle 1986 • Quantifies the change in TOAs due to variations in clocks at the observatory and the SSB due to changes in the gravitational potential of the Earth and the Earth’s motion • Use barycentric corrdinate time (TBC) instead of barycentric dynamical time which was used in tempo1 => tempo1 parameter files can not immediately be used in tempo2 • Note: tempo2 parameters are in SI units …. Tempo1 parameters are not! CSIRO. Gravitational wave detection

  12. Converting tempo1 files to tempo2 • > tempo2 -gr transform 1939_t1.par 1939_t2.par • or • > tempo2 …. -tempo1 CSIRO. Gravitational wave detection

  13. Roemer delay • The vacuum light travel time between the pulse arriving at the observatory and the equivalent arrival time at the SSB • Calculated by determining the time-delay between a pulse arriving at the observatory and at the Earth’s centre and from the Earth’s centre to the SSB • Pulsar positions determined in the ICRS (International celestial reference system). Telescope positions are in the ITRF (International terrestrial reference system). Require precession, nutation, polar motion and Earth rotation information to convert between the two. TEMPO1 does not include polar motion • Use DEXXX or INPOPXX Solar System models for conversion. Recommend DE405. CSIRO. Gravitational wave detection

  14. More tempo2 files • $TEMPO2/ephemeris contains the planetary ephemerides • $TEMPO2/observatory contains observatory coordinates Observatory.dat CSIRO. Gravitational wave detection

  15. Solar system Shapiro delay • Accounts for the time-delay caused by the passage of the pulse through curved space-time • Mainly due to the Sun, but significant Shapiro delay caused by Jupiter. CSIRO. Gravitational wave detection

  16. Dispersive effects • Caused by the ISM - assume delays propto f^-2. • Also dispersive delay caused by the Solar wind. Approximated in tempo2 with the electron density decreasing as an inverse square law from the centre of the sun. • You Xiaopeng developed this model - see You, Hobbs, Coles et al. (2007MNRAS.378..493) and You, Hobbs, Coles et al. (2007ApJ...671..907) CSIRO. Gravitational wave detection

  17. Shklovskii effect and radial motion • Pulsar-timing measurements are affected by the motion of the pulsar relative to the SSB. This includes radial velocity, the Shklovskii effect and radial acceleration. • Can be absorbed by other parameters or included individually CSIRO. Gravitational wave detection

  18. Fitting routines Tempo2 can carry out normal single pulsar fits and also global fits to multiple pulsars CSIRO. Gravitational wave detection

  19. The timing model • Use: • The frequency derivative terms are fitable parameters • Can also include glitch events in the model CSIRO. Gravitational wave detection

  20. Binary models • Have various models implemented from tempo1 (BT, ELL1, DD, MSS …) • Recommend use of T2 binary model • Can assume GR (DDGR model) or small eccentricities (ELL1) CSIRO. Gravitational wave detection

  21. Standard usage of tempo2: Input arrival times • Require a file containing arrival times. Arrival time (MJD) Required Telescope code TOA uncertainty (us) File identifier Observing frequency (MHz) User defined flags CSIRO. Gravitational wave detection

  22. Standard usage of tempo2: Input pulsar model • Require a parameter file (traditionally *.par) Require: PSRJ RAJ DECJ F0 PEPOCH DM MODE 1 = fit with weights MODE 0 = fit without weights SINI KIN => Link the parameters SINI and KIN Each parameter Label value <fit> <error> JUMP -f flag 0 1 FJUMP -f CSIRO. Gravitational wave detection

  23. Standard usage of tempo2 • No plugins: tempo2 -f mypar.par mytim.tim CSIRO. Gravitational wave detection

  24. Standard usage of tempo2 • Using plk: tempo2 -gr plk -f mypar.par mytim.tim CSIRO. Gravitational wave detection

  25. More plugins • Tempo2 -gr spectrum -f mypar.par mytim.tim CSIRO. Gravitational wave detection

  26. The splk plugin CSIRO. Gravitational wave detection

  27. Output plugins: general CSIRO. Gravitational wave detection

  28. Output plugins: general2 • Tempo2 -output general2 -s “Hello: {sat} {post}\n” -f mypar.par mytim.tim CSIRO. Gravitational wave detection

  29. Many plugins exist …. • Plotting • Spectral analysis • Simulating data • Adding noise to data • Adding gravitational wave signals to data • …. CSIRO. Gravitational wave detection

  30. Developing tempo2 • Anyone can create more plugins. • Talk to me if you want to modify the main tempo2 code. • Easiest to use C/C++ and pgplot, but can use other languages/libraries CSIRO. Gravitational wave detection

  31. A very simple ‘output’ plugin • #include <stdio.h>#include “tempo2.h” extern "C" int tempoOutput(int argc,char *argv[],pulsar *psr,int npsr){ int i; printf(“Number of observations = %d\n”,psr[0].nobs); printf(“Name of pulsar = %s\n”,psr[0].name); printf(“A list of site-arrival-times, observing frequencies and residuals\n”); for (i=0;i<psr[0].nobs;i++){ printf(“sat = %g, freq = %g, res = %g\n”,(double)psr[0].obsn[i].sat, (double)psr[0].obsn[i].freq,(double)psr[0].obsn[i].residual); }} See documentation on the tempo2 wiki CSIRO. Gravitational wave detection

  32. Ideas for new plugins • Want to analyse the residuals in a new way (wavelet analysis?) • Want to model the effect of precession in pulsar timing • Want to look for correlated signals in multiple pulsar timing residuals • Want to simulate thousands of realisations of realistic timing residuals • … CSIRO. Gravitational wave detection

  33. Tempo2 demonstration • No plugins • General2 • Plk - plot options, filter, pass, zoom, delete, measure, highlight, turning jumps on and off • Splk • Spectrum CSIRO. Gravitational wave detection

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