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Parameters

Chapter 3: The parameter files

3.1 The basic timing model parameters

The parameter files (that contain the pulsar timing model and various instructions for the tempo2 fitting routines) have the same form as in the earlier tempo implementation. Each of the pulsar parameters has a label, a value and may have an uncertainty on the value and a flag indicating whether tempo2 should fit for this parameter or whether the parameter should be held constant (0 = default = hold constant; 1 = fit). The parameters labels are described in Table 3.1 at the bottom of this page. An example of a parameter file for PSR J0437-4715 taken from the ATNF pulsar catalogue (by selecting the ephemeris option):

 PSRJ            J0437-4715                
 RAJ             04:37:15.7865145       1   7.000e-07 
 DECJ            -47:15:08.461584       1   8.000e-06 
 DM              2.6469                    1.000e-04 
 PEPOCH          51194.000                 
 F0              173.6879489990983      1   3.000e-13 
 F1              -1.728314E-15          1   1.600e-20 
 PMRA            121.438                   6.000e-03 
 PMDEC           -71.438                   7.000e-03 
 BINARY          DD                        
 PB              5.741046               1   3.000e-06 
 ECC             1.9186E-5              1   5.000e-09 
 A1              3.36669157             1   1.400e-07 
 T0              51194.6239             1   8.000e-04 
 OM              1.20                   1   5.000e-02 
 OMDOT           0.016                     1.000e-02 
 START           50640.928                 
 FINISH          52088.897                 
 CLK             UTC(NIST)                 
 EPHEM           DE200                     
 PBDOT           3.64E-12                  2.000e-13 
 TZRMJD          51204.64376750220085      
 TZRFRQ          1413.400                  
 TZRSITE         7                         
 RM              +1.5                      5.000e-01 
 PX              7.19                      1.400e-01 
 SINI            0.6788                    1.200e-03 
 M2              0.236                     1.700e-02  

This indicates to tempo2 that all parameters should be held fixed except for the astrometric parameters (RAJ, DECJ), pulse parameters (F0, F1) and the Keplerian orbital parameters (PB, ECC, A1, T0 and OM). Uncertainties are given on many of the parameters.

In more detail, a pulsar which has a spin period of P0=1.23456 s and no fitting is required then use:

 P0 1.23456 

To request that tempo2 fits for this parameter:

 P0 1.23456 1

or to include an uncertainty on the measurement (which is ignored by the main tempo2 software)

 P0 1.23456 1 0.00003

Other commands may be given in parameter files that control the algorithms used by tempo2. Tempo2 only required the following parameters: PSRJ, DM, F0, PEPOCH, RAJ and DECJ. It is also possible to provide the pulsar parameters in the old-style tempo format where the arrival times and the parameters are given in the same file. Details of this mode (which we do not recommend) are given here.

3.2 Phase jumps

It is often necessary to fit for a constant offset between two sets of arrival times. For instance, the templates used to determine arrival times at different observatories may be perfectly aligned. The command "JUMP" in the parameter file can be used to define such jumps:

JUMP MJD v1 v2 will provide a jump between all arrival times with MJDs between v1 and v2 and all other observations.
JUMP FREQ v1 v2 will jump between observations with frequencies between v1 and v2 MHz and all other observations.
JUMP TEL id will jump between observations at a particular observatory compared with all other observations.
JUMP NAME str will jump on all observations which contains a "str" in the observation identifier.
JUMP flag val will jump on all observations with a specified flag and value.
Examples include

 JUMP -i PKS_DFB 0.234 1
 JUMP FREQ 1400 1500 0 1
 JUMP TEL PKS 0.342

which would initialise a jump for all observations with the "-i" flag set to "PKS_DFB" with the value of 0.234 and then fit for the jump. A jump would be included (and fitted) for all observations with frequencies between 1400 and 1500 MHz and a set (i.e. not fitted) jump would be included on all data observed using the "PKS" telescope.

3.3 Removing timing noise

Even with accurate spin and positional parameters, the timing residuals for some (particularly the young) pulsars contain remnant structures. Some of these structures are understood; cusps, for instance, signify sudden changes in the pulsar's spin rate during a glitch, sinusoidal oscillations can represent unmodelled companions (such as planets) or the pulsar precessing. However, many of the structures seen in the residuals are still not understood and are known as "timing noise". To obtain the most accurate pulsar's positional and proper motion parameters (and dispersion measure) it is essential to remove this timing noise. Traditionally this has been carried out by fitting higher order pulsar rotational derivative terms. However, Hobbs et al. (2004) described an improved method that used the fitting of harmonically related sinusoids.

Such sinusoidal terms can be included in tempo2 parameter files.

 WAVE_OM 0 1
 WAVE1 0 0
 WAVE2 0 0
 WAVE3 0 0

would allow tempo2 to select the fundamental frequency for the sinuosoids based on the data-span (see the algorithm described in Hobbs et al. 2004) and subsequently fit for 3 sine and cosine waves.

3.4 Coping with badly wrong ephemerides

Under normal circumstances, tempo2 should be able to predict exactly the number of turns between any two observations, so that the residual phase error is considerably less than one turn. In early stages of timing a pulsar, during the process of "phase connecting" the data, this may not be true, and phases may "wrap". tempo2 provides several tools to help in this situation.

Most simply, one may add the PHASE command to an observation file. Adding PHASE n tells tempo2 that at that point, n extra phase turns occurred compared to what tempo2 would otherwise assume. Thus PHASE 1 has the effect of adding one full turn to all following arrival times. Naturally as the ephemeris changes the number of turns tempo2 would assume will change, and these will frequently need to be added or removed (hopefully removed).

A more automated approach is to use one of the modes of the TRACK command. TRACK 0 is the default mode of tempo2. TRACK 1 tells tempo2 to assume that the phase error of each residual is within one-half turn of the previous residual, rather than within one-half turn of zero. This only makes sense if the residuals are provided to tempo2 in time order, though tempo2 only warns about this condition. TRACK -1 uses several data points to guess the correct number of turns. TRACK -2 allows a number of turns to be specified for each TOA using the "-pn" flag; it behaves similarly to the PHASE command.

Table 3.1: Pulsar parameters than can be entered in a parameter file

Label Description Units
PSRJ, PSRB or PSR Pulsar name -
FX (e.g. F0, F1, F2) The X'th time derivative of the rotational frequency ($s^{-(X-1)}$)
P0 or P Spin period of the pulsar sec
P1 or Pdot Spin down rate of pulsar ($x10^{-15}$)
PEPOCH Epoch of period determination MJD
RAJ or RA J2000 right ascension hh:mm:ss.sss
DECJ or DEC J2000 declination dd:mm:ss.sss
ELONG or LAMBDA Ecliptic longitude deg
ELAT or BETA Ecliptic latitude deg
POSEPOCH Epoch of position measurement MJD
PMLAMBDA or PMELONG Proper motion in ecliptic longitude mas/yr
PMBETA or PMELAT Proper motion in ecliptic latitude mas/yr
PMRA Proper motion in right ascension mas/yr
PMDEC Proper motion in declination mas/yr
DMEPOCH Epoch of DM measurement MJD
DM Dispersion measure $cm^{-3}pc$
DMX X'th time derivative of the dispersion measure $cm^{-3}pcyr^{-X}$
FDD Frequency dependent time delay
PX Parallax mas
PMRV Radial velocity
- - -
GLEP_X Glitch epoch MJD
GLPH_X Glitch phase incremenet
GLF0_X Glitch permanent pulse frequency increment Hz
GLF1_X Glitch permanent pulse frequency derivative incremenet $s^{-2}$
GLF0D_X Glitch pulse frequency increment Hz
GLTD_X Glitch decay time constant
- - -
WAVE_OM Angular frequency of fundamental sinusoid for whitening
WAVEX Amplitude of sine and cosine for the X'th harmonic for whitening sec
- - -
BINARY Binary model (BT/ELL1/DD/MSS/T2)
A1 Projected semi-major axis of orbit lt-sec
PB Orbital period days
ECC or E Eccentricity of orbit
T0 Epoch of periastron MJD
OM Longitude of periastron deg
TASC Epoch of ascending node MJD
EPS1 ECC x sin(OM) for ELL1 model
EPS2 ECC x cos(OM) for ELL1 model
OMDOT Rate of advance of periastron deg/yr
PBDOT 1st time derivative of binary period s/s or s/s*1e12
A1DOT or XDOT Rate of change of projected semi-major axis lt-s/s or lt-s/s*1e12
SINI Sine of inclination angle
M2 Companion mass Solar masses
XPBDOT Rate of change of orbital period minus GR prediction s/s or s/s*1e12
A1DOT, EDOT or ECCDOT Rate of change of eccentricity
OMDOT Periastron advance deg/yr
PBX X'th time derivative of binary period
GAMMA post-Keplerian gamma term sec
DR Relativistic deformation of the orbit
DTH Relativistic deformation of the orbit
A0 Aberration parameter A0
B0 Aberration parameter B0
BP Tensor multi-scalar parameter beta-prime
BPP Tensor multi-scalar parameter beta-prime-prime
DTHETA Relativistic deformation of the orbit
XOMDOT Rate of periastron advance minus GR prediction deg/yr
EPS1DOT
EPS2DOT
KOM
KIN
SHAPMAX
MTOT Total system mass Solar masses
BPJEP_X
BPJPH_X
BPJA1_X
BPJEC_X
BPJOM_X
BPJOM_X
BPJPB_X
- - -
TEMPO1 Run in tempo1 emulation mode: e.g. use TDB units
UNITS Set units to SI or TDB
MODE Fitting with errors (MODE 1) or without (MODE 0)
JUMP Add a constant offset between specified observations
CLK Definition of clock correction files to use
TRES rms timing residual
NOTRACK Switch off tracking mode
NO_SS_SHAPIRO Switch off the calculation of the Solar system Shapiro delay
IPM = 0 to switch off calculation of the interplanetary medium
NITS Number of iterations for the fit
DILATEFREQ Whether or not to apply gravitational redshift and time dilation to observing frequency (Y/N)
IBOOT Number of iterations used in the bootstrap fitting method
PLANET_SHAPIRO Include calculation of the planetary Shapiro delays
CORRECT_TROPOSPHERE Select whether or not to apply tropospheric delay corrections
NE1AU The electron density at 1 AU due to the solar wind
TIMEEPH Which time ephemeris to use (IF99/FB90)
T2CMETHOD Method for transforming from terrestrial to celestial frame (IAU2000B/TEMPO)
CLK_CORR_CHAIN Clock correction chain(s) to use
EPHEM Which solar system ephemeris to use
TZRMJD prediction (polyco) mode only
TZRSITE prediction (polyco) mode only
NSPAN or TSPAN
TZRFRQ prediction (polyco) mode only
START
FINISH
EPHVER
TRACK

Note that PBBOT, XPBDOT, and A1DOT have special handling: the units are natively s/s or lt-s/s, but if the value is larger than 1e-7, it is scaled down by 1e-12; you may therefore see values like 100 to mean 1e-10.

When PBDOT or other derivatives or orbital quantities are specified, PB, A1 and so on are the binary parameters at the time T0 (not PEPOCH).


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Page last modified on June 03, 2016, at 01:17 AM