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Next: Read spectrum into XSPEC Up: Spectral Calibration of the Previous: The response matrix shift

Calibration Example

  In this section we give an example of how to find the hardness ratio for a source (61 Cyg) in the center of the field, and show how this can be used to constrain the spectrum. We assume that the user is familiar with PROS, FTOOLS and XSPEC.

  1. You will need standard ROSAT archival data products (events and aspect fits files). Run IRAF/PROS and convert them to PROS format.
  2. Use the PROS task qpspec to extract a spectrum from the source of interest. The output of qpspec is 3 files - in the case of 61 Cyg these are,,
  3. Create a FITS file which can be read into XSPEC by running the task provided with this distribution. From within IRAF and in the same directory containing the script type:
    xs> task
    fu> hrifits  rh201950n00
    Here is the input file from qpspec, and rh201950n00 is the root of the output file (``_pha'' will be appended). Note: you must have run the FTOOLS package futils for this script to work. You must have the files ``fitscol'' and ``head'' (part of this distribuion.) The task hrifits will create an output file rh201950n00_pha.fits which can be read by XSPEC. The unshifted ground-based response matrix (hri_dtmat_15.fits) is hard-wired into the FITS header, as is the HRI Ancillary Response File (hri_arf.fits).
  4. Run xgain program to determine BE gain.

    Fill in the parameter file xgain.par:

    # good pars: 48.0 -40.0 0.0  rev0
    #            48.0 -40.0 -0.4 rdf
    EVENTS rh201950n00_bas.fits
    ASPECT rh201950n00_anc.fits
    MAPS   /data/andrea/HRI/jds/gain.fits
    BORESIGHT 48.0 -40.0 -0.4
    TDELAY -0.65
    XPOS 4168
    YPOS 4056
    GHIST 2.0 7.0 0.1
    steps /proj/jcm/Science/hri/hv.dat

    and run xgain. You will need to edit the parameters EVENTS, ASPECT, MAPS, XPOS, YPOS, steps. It may be necessary to edit the other parameters if you are not using RDF files, or are doing more detailed analysis (see Section 4. For 61 Cyg, rh201950n00_bas.fits and rh201950n00_anc.fits are the names of the event and aspect files. These are the FITS files obtained from the HEASARC archive. MAPS contains the location of the gain.fits file your local system, XPOS and YPOS are the coordinates of the source in sky pixels obtained from visual inspection of the image displayed in SAOimage. Finally, steps is the location of the hv.dat file on your local system.

    The output of xgain is displayed to the terminal and written to a file xgain.fits.

  5. Run the script

    This script uses the output of xgain to construct two response matrices. The first is a matrix derived from the ground-based response matrix by shifting it by the ammount corresponding to the mean BE gain of the observation (default name ``new_mean_resp.fits''. The second is a matrix composed of several shifted response matrices, weighted by the time spent in each corresponding gain state (called ``new_resp.fits''.) If the source was not wobbled over too many gain states, the response matrix corresponding to the mean gain is fine. If the source was wobbled over a wide range of gain states the time-weighted response matrix should be used. Note that the spectral resolution can be degraded still further if the source exposure covers many gain states.

next up previous
Next: Read spectrum into XSPEC Up: Spectral Calibration of the Previous: The response matrix shift
Mon May 11 15:21:25 EDT 1998