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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.

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

• Chapter 1: Introduction, obtaining and installing tempo2 and basic examples
• Chapter 2: Required files
• Chapter 3: Parameter files
• Chapter 4: Observation files
• Chapter 5: Running tempo2 and command-line arguments
• Chapter 6: Running tempo2 in predictive mode (polycos and predictor files)
• Chapter 7: Processing multiple pulsars simultaneously
• Chapter 8: The additional graphical interfaces and output formats available
• Appendix A: Developing the software
• Appendix B: Tempo2 error and warning messages
• Appendix C: Frequently asked questions