Use of the Pulsar Timing Programs
The program psrtime takes site arrival times in a variety of formats
and converts them to arrival times at the barycentre (bats), where
they can then be compared with a model of the pulsar timing
parameters. Many quantities in the model can be fitted to the
residuals and information can then be written out in a variety of
sats to bats
In order to carry out the conversion to
the barycentre an ephemeris is required giving such quantities as
position. The ephemeris files are in the format xxx.eph and can be
written out by psrtime, containing those parameters used in the last
fit to the data.
Having read in the sats, they can be sorted into chronological order and then the conversion routine called with the command jplbat. There are other conversion routines but they have been superceded.
The program no longer requires you to define which pulsar to process, but
will assume that all the data belongs to the same source (this is to allow
analysis of a source under slightly different names!)
After bats have been written out for the first time together with an ephemeris file, a file is created called psrav.dat. This file contains psrtime commands and can be read back into psrtime with the obey command to set the source name ,read an ephemeris, read the bats and set the start and finish time to cover all data. The value of -1 instead of a specific date for start and finish will set those quantities to the first and last times in the data.
Using the GUI
The most used command is cursor which enables a Graphical User
Interface (GUI) for displaying the residuals and fitting various
quantities to the data etc. At all times the middle mouse button will
show in the top right hand corner a snapshot of the pulse profile of
the point nearest the position of the cursor. This is obtained from a
file <file>.pro which was produced by psrprof at the same time as
producing the file <file>.tpo using the command obey psrav2.com. Also
the right hand mouse button will delete the nearset point. Note that
the data has not been erased, but only flagged as deleted, the button
restore all bats will negate the action of those flags. If there are
many points that need to be deleted then when they have been selected
they can be written to a file <file>.del, which will automatically be
read on and obeyed in the start up file.
The standard file name is psrav (to indicate that the data has been obtained with the averaging format in psrprof), hence there will be psrav.tpo, psrav.pro, psrav.eph, psrav.bat and psrav.del.
There are many quantities that can be fitted in the model, the first
set are the normal slowdown parameters, epoch, period, first and
second period derivatives. A third derivative can be set but not
fitted for. All these quantities can be entered as either period or
frequency, the difference being in the units used, i.e. set period 30
hz is setting a frequency, but set period 0.033 secs is setting the
period. Thereafter in the program both quantities are stored. The next
set of quantities are dispersion measure and its time derivative ddot,
ra and dec and their proper motions. There is also a full set of
binary orbital parameters that can be fitted as well as
exponentials. Note that although three exponentials are available only
two can be fitted. Therefore the command swap exponential will swap
the parameters of the given exponential with the parameters of the
third exponential. In a similar manner with binary parameters,
although three sets of binary parameters are available only one can be
fiited, hence swap binary will swap the required set with the first
The other buttons carry out the following operations:-
The square boxes are check boxes and are set on for required operation, i.e. those quantities to be used in a fit. The round circles are radio controls and only one in a particular area can be on at any one time, in general these define what the action is when the left hand mouse button is pressed.
In general they are self explanatory, the start and finish define the time interval over which one wishes to plot or fit, rectangular delete will delete all points within an area bounded by two points. The epoch can be set at any point on the plot, this in fact does an update epoch to that date, or the button Centre can be pressed when the epoch will be set midway between the first and last data points on the screen. Bat id gives details of the nearest point to the cursor, this can be done at any time with the middle mouse button. zoom and unzoom will be centred on the point of the cursor.
Next there are some options as to how to display the data or where to send it. plot will just plot the current data, and this can be against either phase or epoch, obviously against phase has no meaning unless it is a binary pulsar. Full plot with the all data check box on will display all the data that was in the bat file, for the Crab this is a lot of points. There is also a little plot produced above the main plot which always shows all the data between start and finish when starting cursor, hence even if one zooms in and out etc, this will still show all that data, making it easier to reset start and finish outside the current plot. If the To file box is on then when hitting plot the residuals will be written to a file <file>.res, and if the hardcopy box is on then a postscript file called <file>.ps will be generated for that plot.
Remove wave is a specialised facility, used for removing long term timing noise for examination of proper motion etc.
The last set of buttons are very important allowing transfer of data
with the outside world. Having obtained the best fit to the data a new
ephemeris can be written out, using the WR NewEph button, there are
safeguards built in to check in case you are potentially overwriting
an existing ephemeris. The other output is WRCorrect. This will output
the ephemeris to a file called correct.dat, which has a format so that
it can be read into psrprof to correct the data from the online
ephemeris to this new one. It is suggested that as soon as this file
is written it be renamed as the next file will also be called
correct.dat. There are two other buttons Wr Del and Rd Del, these
will write to and read from a file called <file>.del those points that
have been deleted. The last button that is used is WrTempo, this will
write out the fit in a format that can be read by the tempo program
for producing an ephemeris for copying to the pulsar public ftp area.
|May 8, 2001||caj|