*period* - Period search using epoch folding

Search for periodicity using the timesorted output file.

This task determines the period which produces the folded light curve with maximum deviation (i.e. chi sq) from that of a constant source. It outputs the folded light curve as a function of phase in rp90_sec2_fld.tab, and the run of chisquare vs. period in rp90_sect2_chi.tab.

The sample interval must be set short enough so the sampling is complete. To search for a period pseconds in an observation of length t seconds, sorting into n bins, the period interval, $\Delta p$, should be $\Delta p = p^{2}/nt$. If the user specifies a period increment of ``0'', the computer will calculate this interval.

The parameter get_gintvs=yes requires that an exposure be calculated for each interval, important if the period is comparable to the duration of gaps and good-data intervals.

input file: rp90_sect2_sti.qp

output files: rp90_sect2_fld.tab, rp90_sect2_chi.tab

  xt> period.pdot=4.22e-13    # enter value of period derivitive (units, s s-1)
                                                     # if known.  Default is 0.

Note: For those sources with a period which changes linearly with time, enter dp/dt value (4.22e-13 is the value for the Crab pulsar).

  xt> period
  Input Source Timing File: rp90_sect2              # assumes extension _sti.qp
  Input Background Timing File:  none
  Root name for output files [root_fld.tab, root_chi.tab]:  rp90_sect2
                                              # Assigns name rp90_sect2_fld.tab
  Period start:  90                                         # units are seconds
  Period stop:  110
  Increment (0 for auto increment):  0.1
  Number of bins:  10       # trial periods will be divided into 10 phase bins.

Results may be viewed using

  xt> chiplot rp90_sect2_chi                                # command line mode