ROSAT

Xselect is the environment which allows you to examine ROSAT files (in addition to several other missions, including ASCA). The following is a list that gets you started with xselect:

• xselect invokes xselect, prompts for name of session.
• read events prepares to analyse file. You are prompted for the file's name and location (path), and whether you'd like to change a mission.
• set device [/xw;/ps] changes output destination to either /xw or /ps.
• extract curve extracts an energy (not power) spectrum of a current FITS file
• extract spectrum extracts a light curve from the current file
• plot [stuff] plots the current extracted object. For instance, you can plot an extracted light curve with plot curve
• rescale xmin xmax serves the same purpose as it does in lcurve and powspec.

Figure: Example GK Per light curve extracted from ROSAT data. The upper figure shows the full dataset (some rescaling is required), while the bottom shows a gap free portion of that dataset (after more rescaling).

Figure: Example energy spectrum from the same data set. Compare with the EXOSAT spectrum in figure 7.

A typical xselect session may go as follows. Suppose you want to view the light curve and energy spectrum of GK Per. You would go to the directory
tutorial/ftools/gkper/rosat/rp300217n00. Then:

• Type xselect, and call your session sess1.
• Type read events. Type ./ for the directory, rp300217n00_bas.fits as the file, and yes to change the mission from ASCA to ROSAT. So far, your session should would look like this:

  % xselect
   
                           **  XSELECT V1.4   **
   
  > Enter session name >[xsel] sess1
   
   Notes: XSELECT set up for      ASCA
   Keywords for time and pha are  TIME       
   Units of time are              s
   Default timing binsize =   16.000
   
  sess1:ASCA > read events
  > Enter the Event file dir >[./] ./
  > Enter Event file list >[rp300217n00_bas.fits] 
  Got new mission: ROSAT
  > Reset the mission ? >[yes] 
   
   Notes: XSELECT set up for      ROSAT
   Keywords for time and pha are  TIME       PI
   Units of time are              s
   Default timing binsize =   16.000
   
   
  Setting: IMAGE binning    =   15
           WMAP binning     =   15
           Energy Column    = PI
           Energy rebinning =    1
           Image keywords   = X          Y
           WMAP keywords    = DETX       DETY
   
   
  Getting Min and Max for Energy Column...
  Got min and max for PI:     1    500
   
  Could not get minimum time resolution of the data read
  Number of files read in:   1
   
  ******************** Observation Catalogue ********************
   
  Data Directory is: /astro/a5/vjacobs/docs/tut/gkper/rosat/rp300217n00/
  HK Directory is: /astro/a5/vjacobs/docs/tut/gkper/rosat/rp300217n00/
   
   
          INSTRUME OBJECT   DATE     RA_NOM   DEC_NOM  ROR_NUM  LIVETIME
        1 PSPCB    GK PER   24/04/96 0.53E+02 0.44E+02   300217 0.21E+05
   
  sess1:ROSAT-PSPC >
  

• Type set device /xw
• Type extract curve
• Type plot curve. At this point you should see a light curve.
• Type hardcopy /ps, if you want a hardcopy (don't forget to change the name of the pgplot.ps file, as this file gets overwritten).
• Type extract spectrum to get the energy spectrum of this source
• Type plot spectrum to get a plot of gk per. Rescaling may be very helpful!

$\circ$ Exercise 5: Use xselect to generate a sample light curve and energy spectrum of the source AM Her. The file is: the second PSPCB file in the ROSAT X-ray archive (data set:RP300067A00, exposure:11647 sec). If you click on basic science events and retrieve data products, you'll download the file rp300067a00_bas.fits.Z (after de-tarring). Use xselect on the file rp300067a00_bas.fits, and don't be afraid to rescale and save hard copies. For example, the first light curve you'll make will contain about 18 groups of data separated by gaps. Rescaling will be crucial to interpreting this plot.