We will do some analysis of PN Timing data of the high mass X-ray binary GX
301-2 (Obs ID 0555200301) with Xronos, which is a powerful timing analysis software
package available through the HEASARC. More about Xronos can be found here:
We will assume that the data has been reprocessed with SAS, and a light curve
with time bin size of 1 second was made with SAS and named pn_ltcrv.
Xronos does not have a GUI, so all tasks will be called from the command line.
In the examples below, all the tasks prompt the user for further information.
Input that we've been prompted for is shown with the indented lines.
Let's start by pulling up a new window and invoking ftools:
The task powspec calculates the power spectrum density for a given
time series, plots the result, and writes the results to a FITS file. We can
use the recommended defaults as a starting point.
powspec pn_ltcrv.fits - 25 4096 1 0 [enter] [enter] [enter]
The output is shown in Figure 15.1. We can zoom in on
a region of interest by resetting the axis minimum and maximum. To quit the
plotting software, just type 'exit'.
We can also do this with geometric rebinning:
powspec pn_ltcrv.fits - 25 4096 1 -1.01 [enter] [enter] [enter] exit
The output is shown in Figure 15.2.
We can also search for the source's period with the task efsearch. The period
was determined by Furst et al. (2011, A&A, 535A, 9) to be 685 s, so we will use that
as a starting point.
efsearch pn_ltcrv.fits - INDEF 685 8 689 4 128 [enter] [enter] [enter] exit
The output is shown in Figure 15.2. efsearch automatically
indicates the best period and resolution at the top of the plot, with the bin
size on the upper right side.
The task efold will produce a folded light curve.
efold 1 pn_ltcrv.fits - INDEF 689 10 857 1 [enter] [enter] [enter]
We can add a line to the plot to make it easier to see.
line step p
And color, if we are feeling fancy. In the statement below, "3" refers to
the color choice and "2" refers to the data on the Y axis. If we wanted to
turn off the error bars, we could also enter the command error off.
color 3 on 2 p exit
The plot is shown in Figure 15.4. By default, the folded period
is shown in the upper right part of the plot.