@begin(header)
author: Eric Mandel
show_author: ShowNone
author_organization: Smithsonian Astrophysical Observatory
node_expert: assist_xray@cfa.harvard.edu
expiration_date: 12/31/93
last_modifier: eric@foobar.mit.edu
last_mod_date: 12/05/92
mod_num: 5
@end(header)
@b<PROS Tutorials: Timing>

As an example we use the Einstein Observation of CTB109, a supernova
remnant with bright internal pulsar. Data are found in the PROS
package directory "xdata".  This tutorial will lead you through some
basic tasks in the PROS spectral package. It assumes that you already
are set up to run IRAF and that your @b<imdir> directory exists.

Load the @b<xray> package:
@button<xray, @dynamic[SendString,iraf,task,xray]>

Load the @b<xtiming> package:
@button<xtiming, @dynamic[SendString,iraf,task,xtiming]>

First the source events are extracted from the rest of the field using
a circular region centered on the source.  Events will be time ordered
in the output file:
@button<timsort xdata$snr psr 'c 503 513 24' none, @dynamic[SendString,iraf,task,timsort xdata$snr psr 'c 503 513 24' none clobber+]>

A light curve is then generated and plotted so we can inspect the
gross properties of the sample (the sequence of good-data intervals
and gaps) and any source variability:

Create the light curve:
@button<ltcurv psr none psr 500, @dynamic[SendString,iraf,task,ltcurv psr none psr 500 clobber+]>

Plot the light curve:
@button<ltcplot psr_ltc, @dynamic[SendString,iraf,task,ltcplot psr_ltc]>

To exit the plot program:
@button<q, @dynamic[SendString,iraf,task,q]>

Finding this sample satisfactory, we search for periodicity with a
fast Fourier transform. We use 2**14$ bins so the search will cover
periods >= 1 in this 7700 s data interval.
@button<fft psr_sti.qp none psr src 0 16384, @dynamic[SendString,iraf,task,fft psr_sti.qp none psr src 0 16384 clobber+]>

The result can be viewed by plotting power as a function of frequency:
@button<fftplot psr_fft, @dynamic[SendString,iraf,task,fftplot psr_fft]>

To exit the plot program:
@button<q, @dynamic[SendString,iraf,task,q]>

It can also be viewed by listing the table containing significant coefficients:
@button<timprint psr_pwr 1--25, @dynamic[SendString,iraf,task,timprint psr_pwr 1--25]>

We find significant power at low frequency because of the gaps in the
data record and, at a frequency of 0.2868/sec, the pulsar.
The period can be verified and measured more precisely by epoch
folding over a range of trial periods.
@button<period psr none psr 3.45 3.50 0.0003 5, @dynamic[SendString,iraf,task,period psr none psr 3.45 3.50 0.0003 5]>


The result can be ploted and listed,
@button<chiplot psr_chi, @dynamic[SendString,iraf,task,chiplot psr_chi]>
@button<timprint psr_pwr  110--150, @dynamic[SendString,iraf,task,timprint psr_pwr  110--150]>

and shows the period to be 3.4890 s (freq=0.2866).  A folded light
curve for the most promising period is also generated and can be
viewed.
@button<fldplot psr_fld, @dynamic[SendString,iraf,task,fldplot psr_fld]>

We are finished.  We have the period and pulse shape.  This example
uses a strong source with rather slow period (the real period is
actually 6.978 s).  In practice it is usually necessary to use
barycenter-corrected data and much longer Fourier transforms.  The
following sections give more detail for each task.

(THIS IS THE END OF THE TUTORIAL.)