pcbgdcor -- correct ROSAT background spectrum
While it is often possible to select a background spectrum from a source-free region close to the target of interest, occasionally it is necessary to extract the background spectrum from a different part of the detector. In the latter case the background spectrum requires some correction before it can be subtracted from the source spectrum. This is because there are variations across the detector face due to vignetting, exposure variations and a gradient of the particle background (different to the gradient due to vignetting). For these reasons, background spectra should be "corrected" appropriate to the region from which the source was extracted (not necessarily on-axis itself). Users taking source and background spectra from similar regions on the detector need not perform this correction (for example, spectra taken within 10' of the center of the field, when the source is observed on-axis need not be corrected). This tool does not correct for gradients of the scattered solar X-ray background which sometimes varies significantly across the detector face.
The task assumes the user has extracted source and background spectra from xselect, and will require the image upon which region files were defined (save from xselect) as well as the region files themselves, the events file, event rate file and corrected aspect file. *warning* if the user has made a time selection for extraction of the spectrum (e.g. used only the first half of the observation) then a similarly time-filtered events file should be used with the task.
This script first calculates the particle background components of the source and background spectra by running PCPARPHA. Then it runs PCARF to create the ARF files for the source and background spectra. Arfs are not usually created for background spectra, they are used here to calculate one component of the correction (the arf for the background file cannot and should not be used in xspec). Next the script runs PCEXPMAP to get the exposure correction needed and FIXREGION to convert the region file to the exposure map coordinates, so that exposure correction is done for the particular source region. Now, CALCBGDCOR collects all the elements of the correction and performs the correction of the input background spectrum to be approriate for the input source region.
To run the script, one has to type pcbgdcor on the command line. (One can also type the input files required for the task, but there are a large number of files to be typed). Input files are the events file, eventrate file, attitude file, source and background spectra and their respective region files along with image file saved from xselect.
-h print help information and do not execute.
-v {#} verbose, helps locate any problem running the script.
-a {file} Input source spectrum file
-b {file} Input background spectrum file
-c {file} Input event rate file
-d {file} Input ATT file
-e {file} Input EVENTS file
-f {file} Input ARF file for source
-g {file} Input ARF file for background
-i {file} Input source region file
-j {file} Input background region file
-k {file} Image file saved from xselect
Help on CALCBGDCOR
v1.0.0 (Sept, 1996) first release
Banashree Mitra Seifert
HEASARC, NASA/GSFC
http://heasarc.gsfc.nasa.gov/cgi-bin/ftoolshelp