FTOOLS 4.0 UPDATE #1: ROSAT PACKAGE UPDATE
WHERE TO GET THE UPDATE:
The FTOOLS update can downloaded via anonymous FTP from: legacy.gsfc.nasa.gov
or via the WWW from: ftp://legacy.gsfc.nasa.gov/rosat/software/ftools/ftools.v4.0_update1.tar.gz
The tar file contains the files README.UPDATE1 and INSTALL.UPDATE1 as well as the actual patch.
DESCRIPTION OF UPDATE
- If you use the script PCPICOR to correct your PSPC data, then you are using PCECOR and you need this patch ***
Progress has been made on understanding and correcting residual variations in the temporal and spatial gain of the PSPCs. A subroutine has been added to the ftool PCECOR to correct for the temporal- and energy-dependent gain variation discussed in Prieto, Hasinger, and Snowden (1996, A&AS, 120, 187). PCECOR allows users to correct the PI assignment of PSPC events for the variation in the linearity of the PSPC response with absolute gain. This tool became necessary because it was observed that the effective gain in the 0.25 - 1.0 keV energy range was lower than expected after normalizing to the 1.5 keV calibration-monitor line, and this effect became worse with lower absolute gain (for example, a 0.75 keV X-ray might be detected as a 0.72 keV X-ray when the PSPC was operating at low gain). However, a bug in the PCECOR ftool has resulted in too small a correction being applied to the PI channel. This bug has now been fixed and the alternative correction algorithm, based on the Prieto paper, has also been incorporated into the tool.
In the new version, users can choose from one of two options for the PI correction:
- Using calibration data from the PANTER facility in Neuried. The data were collected several years after the launch of ROSAT, using the engineering-model PSPC. Data from calibration lines (covering the PSPC energy range) allowed a check of response linearity over an extended energy range.
- Using in-flight observations of calibration sources (such as N132D) to determine the PI correction as a function of time. See Prieto, Hasinger and Snowden (1996) for details.
Method 1 was the only option available in all previous versions of PCECOR. However, a comparison shows that method 2 produces significantly better results for data taken during the later epochs of PSPC data (1994). In combination with tasks to fix the SASS spatial gain correction bug the fits to data from constant-spectrum sources observed at several times throughout the mission show considerably greater self-consistency with the new version of PCECOR, using either method 1 or 2. This is particularly true for the LMC SNR N132D whose spectral characteristics were the most sensitive to the residual gain variations. We provide both correction algorithms so that users may have all options available to them. A paper discussing these data-corrections will be made available as soon as it is accepted for publication.
The time dependant calibration correction is taken from the AlK calibration
file closest to the users observation. Previous versions of the task used
8 calibration files:
The new version of pctcor, v1.1.0, utilizes 13 files in place of the original 8.
The new files allowed a more accurate time-dependant calibration correction, since they encompassed AlK data covering a larger fraction of the PSPC lifetime.
The perl script PCPICOR calls PCECOR as the last part of the PSPC data-correction procedure. A new version of PCPICOR is required, as the user interface has been updated to allow the selection of data-correction algorithm for PCECOR.
PCFILT / HRIFILT
A problem was also found with the dec alpha versions of PCFILT and HRIFILT. There was a bug which caused those tools to have a segmentation fault under under some circumstances.
A bug has been fixed which caused RBNRPSF to set the wrong area-weighting, under some circumstances (this bug did not affect the radial profile data, but ultimately resulted in a mismatch between the psf model normalization and the data further down the data-analysis pipeline, in the output from HRIRPSF).
The perl script srcdetect had a typographical bug.
This routine now allows the user to compare the psf model and data without the use of a pha file (which allows a counts weighted model to be generated). In the absence of a pha file, a mean psf model is calculated assuming uniform weighting over the PSPC energy range. The code also allows the user to bypass the wmap, even if a pha file is used. This allows a very fast run of the program, although not as accurate as a full consideration of the wmap weighting.
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