RXTE GOF |
Creating HEXTE Responses Recipes from the RXTE Cook Book |
RXTE FAQ |
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- Definitions & requirements
- The shortcut method
- Using hxtrsp to make a response (recommended)
- Relevant links
In the case of the HEXTE, the response depends primarily on:
Spectra produced by SEEXTRCT/SAEXTRCT do not have a DETNAM keyword. It is
strongly recommended that users add this keyword to the FITS headers of
their spectra before using them with calibration files.
For ease of use with the CALDB (see later) and XSPEC, Cluster A spectra
should have a DETNAM keyword set to "PWA". For cluster B, an additional
complication is due to the loss of spectral capability from detector PWB2 in
1996 March 6 11:27:12 UT. Thereafter, all the counts from this detector end
up in PHA channels 1 and 2. Before this date, Cluster B spectra should have
DETNAM set to "PWB". After this date, the use of detectors 0, 1, 3 only is
denoted by DETNAM="PWB013". This affects both the RMF and the ARF.
You can easily set the DETNAM keyword using the Ftools; one method is to
use fparkey:
Definitions & requirements
Following OGIP convention, HEXTE response matrices are notionally divided
in two parts: the Ancillary Response File (ARF), which accounts for
the detector windows and collimator response; and the Redistribution
Matrix Function (RMF), which accounts for the redistribution of photon
energy amongst detector channels by the detecting medium. The product of the
two is known as the response (RSP) and is used by XSPEC for spectral
analysis.
fparkey add=yes "PWA" FS50_xxx.pha DETNAM
fparkey add=yes "PWB013" FS52_xxx.pha DETNAM
(The script hxtrsp described below will also set these keywords for
you).
The shortcut method
If you are in a hurry, and/or you do not have the HEXTE files installed in a
CALDB on your system, you can retrieve the following HEXTE cluster
A and B rmfs and arfs from:
ftp://legacy.gsfc.nasa.gov/xte/calib_data/hexte_files/DEFAULT.
These files are adequate for analysis with XSPEC, assuming the following conditions:
- You are sure that the data were obtained with the source close to
the RXTE pointing axis (fplot the OFFSET values in the XTE filter
file to verify).
- You are sure that the data were obtained after 1996 March 6 11:27:12 UT when Cluster B detector 2 lost its spectral capabilities.
- Your spectra have the full 256-channel sampling. (e.g. most Event
data). If not (e.g. Standard Modes data has been rebinned to 64 bins),
then these matrices must be rebinned to match the PHA file thus:
fparkey add=yes "PWA" hexteA.pha DETNAM rddescr phafil=FS50_xxx_src.pha chanfil=FS50_xxx.bins rbnrmf binfile=FS50_xxx.bins infile=hexte_97mar20c_pwa.rmf outfile=FS50_xxx_src.rmf fparkey add=yes value="FS50_xxx_src.rmf" fitsfile=FS50_xxx_src.pha keyword=RESPFILE
However, if you have the HEXTE calibration files installed in the CALDB, it is much easier to use the hxtrsp script to perform these steps (with an attitude file of "NONE" if condition 1 above is satisfied).
Using hxtrsp to make a response (recommended)
Note: Before running hxtrsp, you must have a CALDB installed on your system.
Attention GO's with an offset pointing!!! |
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In the special case of a requested offset pointing, you will need
to modify the keywords in the header BEFORE running hxtrsp. The keywords
RA_OBJ and DEC_OBJ contain the coordinates of the pointing requested; use
fkeyprint or fdump to inspect their values in the PHA file.
For an offset pointing, these should be changed to the SOURCE coordinates
using fmodhead as in the following example:
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Running hxtrsp:
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hxtrsp is a Perl script installed under the Ftools
environment. To invoke the script, just type "hxtrsp". Optional
command-line inputs are:
hxtrsp -h (provides help information) hxtrsp -i pha_file -a attitude_file (specifies the input files)Enter the name of the PHA file. If you have not yet set the DETNAM keyword, hxtrsp will prompt you for its value and write your input into the PHA file before proceeding further. This will ensure that the corresponding calibration data can be found in the CALDB.
Enter the name of the file containing the RXTE spacecraft attitude information. To compute the collimator response correctly, hxtrsp needs this information. It can be found either in your filter file or in the quaternion file (the file beginning with "FH0e_"). These files are the same as those used by the pcarsp script for PCA data.
However, if you don't have the attitude information and are confident that the source was observed close to the RXTE pointing axis, you may enter "NONE" and hxtrsp will still work correctly.
hxtrsp will then generate an RSP file with the same root name as the PHA file, and extension ".rsp". This file name will also be written into the PHA file for use with XSPEC.
For those interested, hxtrsp generates the response with these steps: (i)> retrieving the appropriate RMF from the CALDB, (ii) rebinning the RMF (if necessary) to match the PHA file, (iii) retrieving the on-axis ARF and the collimator response from the CALDB, (iv) using these to form an ARF corrected for the off-axis angle, and (v) combining the RMF and ARF to produce an observation-specific response (RSP).
Relevant links
- HEXTE
calibration news, including template spectra of the Crab (at UCSD).
- RXTE
cross-calibration status, comparing the HEXTE and the PCA responses.
If you have a question about RXTE, please send email to one of our help desks.