ROSAT Guest Observer Facility

ROSAT Status Report # 86

March 1, 1994


Contents


ROSAT Satellite Status

ROSAT is presently in a test phase during which its behavior in a stabilized operating mode is being studied. In this mode, the satellite is angular-momentum stabilized if no starsensor information is available in the shadow. In this case, the magnetometers (the sources of the irregularities) are not used by the control procedure.

This stabilized mode has now been tested for almost a week and has proven very stable. MPE decided to continue with the observing program starting around midnight (UT) of Feb. 26/27, at that point the timeline switched over to 5 days of PSPC observations. Re-starting the observing program with the PSPC, MPE will be able to continue the monitoring of ROSAT's behavior for another 5 days before they resume observations with the HRI on March 4.


Update on ROSAT naming conventions

This section is a follow-up to http://heasarc.gsfc.nasa.gov/docs/rosat/status/status76.html ROSAT Status Report #76, which described the conventions employed in naming ROSAT observations and processing software versions. That report contained the following diagram (here updated) to illustrate the situation:


time     SASS 3_0         Rev 0         U.S. FITS           RODFITS
 ||          |              |               |                (MPE)
 ||          |              |               |                  |
 ||      SASS 5_9           |               |                  |
 ||    ------------ - - --------- - - ----------- 27 Jan 93 ---------
 ||      SASS 6_0         Rev 1             |                  |
 ||          |              |               |                  |
 ||          |              |               |                  |
 ||      SASS 6_9           |               |                  |
 ||    ------------ - - --------- - - ----------- ~1 Mar 94 ---------
 ||      SASS 7_0         Rev 2            RDF >---->+<-----< RDF
 ||          |              |                        |
 ||          |              |                       RDF
 ||          |              |                        |
 ||          .              .                        .
 ||          .              .                        .
 \/          .              .                        .

Standard Analysis Software System (SASS) versions used to process ROSAT data are characterized as Revision 0 ("Rev0"), Revision 1 ("Rev1"), or Revision 2 ("Rev2"). SASS versions 3_0 to 5_9, which were used prior to January 27, 1993, are called Rev0; while SASS versions 6_0 through 6_9, which were used from Feb. 1993 to Jan. 1994, are called Rev1; and SASS version 7_0 and up, used after Feb. 1994, are called Rev2.

The new RDF data-product format (Rationalized Data Format, introduced 1994 March) unifies the different German and U.S. FITS formats into a single set of formats. All data processed prior to 1994 January (regardless of whether processed with Rev0 or Rev1 SASS) will be re-processed using the latest Rev2 SASS software and formatted into RDF data products. Observations performed after 1993 Dec 22 will be not require re-processing since they will be initially processed with Rev2 SASS software and formatted directly into RDF data products. Hence all data in the public archive will eventually be replaced with Rev2-processed, RDF-formatted data products, resulting in a uniform public archive of all ROSAT observations.


PROSCON update:

With IRAF/PROS version 2.3 (released 1993 December), output from the task "qpspec" (in the xspectral package) has been changed to conform to the recommended RDF FITS standards. The source and background off-axis histograms are now in files (*_soh.tab and *_boh.tab, respectively) separate from the spectral data (*_obs.tab). To permit use with old versions of XANADU/XSPEC, the new PROS spectral files can be converted back to old-style spectral file format using the xspectral task "downspecrdf". This change initially led to some problems with "proscon" (which required an IRAF/PROS work-around - if you need this contact: hotseat@cfa.harvard.edu), but proscon now has been modified to handle files produced by downspecrdf (so now you don't need the PROS patch).

A tar file containing the new version of proscon has been placed on "heasarc.gsfc.nasa.gov" anonymous ftp, under:

/rosat/software/fortran/proscon/proscon_sun.tar.Z

An alternative work-around for this file conversion is to use the IRAF task stsdas.fitsio.stwfits to dump the PROS "qpspec" output files to FITS files and then use ftools.caltools.stw2pha to make a FITS pi file for XSPEC. This technique has the advantages of producing an OGIP FITS-format pi/pha file and allowing conversion of HRI spectral files. This technique does not make a response matrix. ROSAT FITS matrices are available on heasarc.gsfc.nasa.gov under /caldb/data/rosat/pspc/cpf/ and from /caldb/data/rosat/hri/cpf/ (where cpf means calibration product file). The disadvantage with the using ftools route is that it currently can only be used for sources within a few arcminutes of the detector center (the folding-in of off-axis corrections is under development and will soon be available).

As noted in ROSAT Status Report # 74, FTOOLS are a collection of utility programs to create/modify or examine data files in the FITS format. FTOOLS form the basis of the ASCA analysis system, but there are a large number of general FITS tools which are useful for the analysis of ROSAT data, along with an increasing number of ROSAT-specific tasks. The FTOOLS tasks run either standalone on all common platforms, and/or can be installed as an IRAF package. At the current time, it is recommended that the caltools subpackage of FTOOLS be run outside of IRAF to avoid memory allocation problems.

The latest FTOOLS release version can be found as compressed tar files in the /software/ftools/release/ directory of the anonymous ftp account on heasarc.gsfc.nasa.gov.


PROS -> XSPEC SUMMARY:

In PROS 2.3, qpspec produces seq_obs.tab, seq_soh.tab, seq_boh.tab
  1. If the source is within a few arcminutes of the detector center use:
    STSDAS.FITSIO. STWFITS -> seq_obs.stwfits, seq_soh.stwfits,seq_boh.stwfits
    STW2PHA-> seq_obs.pha (FITS)

    (This route allows conversion of PSPC and HRI files. STW2PHA can be run outside of IRAF or from FTOOLS.CALTOOLS, the former is highly recommended, to avoid memory allocation problems - see above).
  2. If the source is off-axis use:
    seq_obs.tab, seq_soh.tab, seq_boh.tab -> xray.xspectral.downspecrdf
    -> seq_prdf_obs.tab

    proscon seq_prdf_obs.tab
    ->seq_prdf_obs.pha (SF)

    (PSPC only, the output file is binned to 34 channels and is of old SF format, and you must use the new version of proscon, see above)

Comparisons between X-ray spectral fitting packages XSPEC and PROS

There are differences between PROS and XSPEC that have been traced to differing assumptions in the default models. In particular, results obtained with XSPEC's "wabs" and "raymond" models are NOT directly comparable with PROS.

However, meaningful comparisons between PROS and XSPEC, using the Raymond model with finite absorption, can be made by tailoring XSPEC to the abundance and absorption values used by PROS. This can be done by setting the XSPEC abundance ratio = 1.26 in versions of XSPEC prior to 8.4.

Galactic absorption in both XSPEC and PROS is approximated as a piecewise cubic polynomial. Wabs in XSPEC and abs in PROS use identical coefficients for the polynomials. PROS determines the absorption based on the central energy in a given PI bin. XSPEC performs a different numerical approximation when there is an edge within a given PI energy bin. The differences between the two models is only noticeable in soft, highly- absorbed spectra around the carbon edge. The difference is only about 3% which is less than the systematic errors in the PSPC response matrix at the Carbon edge.


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Curator: Michael Arida (ADNET); arida@milkyway.gsfc.nasa.gov
HEASARC Guest Observer Facility


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