NAME

ftrbnrmf -- Physically compresses (rebins) an RMF dataset in channel-space and/or energy space.

USAGE

ftrbnrmf infile [ebdfile] cmpmode [ecmpmode] [binfile] [phafile] nchan [ebinfile] [ebfact] outfile [clobber]

DESCRIPTION

FTRBNRMF compresses a FITS RMF matrix (redistribution matrix file in an OGIP-standard format) in channel-space and/or energy-space to give a user-defined number of resultant channels and energy bins. The output is a new file containing the revised (compressed) MATRIX extension, and the corresponding EBOUNDS extension containing the nominal energies of the revised set of channel boundaries.

Caution is urged before FTRBNRMF is used. The primary use of the task is likely to be to compress RMF datasets in channel-space such that the resultant number of channels matches that in a given PHA dataset. Hence downstream spectral analysis packages can be used to unambiguously map the channels in the PHA spectrum and Response matrix. The binning can be either defined via a text file using the hidden binfile parameter, from a grouping column in a pha file using the hidden phafile parameter or using a specific mode (or 'type') of compression defined by the cmpmode parameter.

CHANNEL COMPRESSION MODES

The following modes of compression (only) are currently allowed when binning in channel-space :

cmpmode='binfile'
Read the binning information from the filename specified by the binfile parameter. This can be used to perform different linear compressions over different channel ranges.

cmpmode='phafile'
Read the binning from the GROUPING column in the filename specified by the phafile parameter.

cmpmode='linear'
In most cases (ie for most instruments & operating modes) only a linear compression is allowed. The compression is such that for a given compression factor F (calculated from the number of channels in the original RMF extension and the number requested by the user), the data applicable to channels 1 to F of the original RMF matrix will be co-added to form channel 1 of the new matrix, channels F+1 to 2*F of the old dataset channel 2 of the new matrix etc. The number of channels requested in the output file should be a factor of the number of channels in the input file.

cmpmode='bright2linear'
This is a non-linear compression mode which should only be used on an ASCA SIS RMF which has the 'non-linear' channel-numbering scheme appropriate for 'BRIGHT' datamode data, but which the user wishes to use in conjunction with a PHA file from the same instrument constructed whilst the instrument was operating in another datamode (such as the SIS 'FAINT' datamode). In the 'BRIGHT' datamode SIS PHA spectra have only 2048 channels (compared to 4096 PHA channels available within SIS 'FAINT' datamode). This is is achieved by a non-linear binning-up the PHA dataset carried out on-board ('FAINT' channels 1024 -> 2047 are binned by a factor 2 by the on-board electronics, and 'FAINT' channels 2048 -> 4096 by a factor 4). RMFs constructed for use with 'BRIGHT' datamode data therefore are similarly rebinned and hence have a 'non-linear' channel-numbering scheme. The mode is designed to compensate for this fact, and linearize the channel-number scheme such that it is appropriate for PHA datasets collected whilst the SIS was not operating in 'BRIGHT' datamode. Thus, FTRBNRMF calculates and applies three separate compression factors (F1, F2 & F3) to the input RMF dataset over the input channel ranges 1 -> (Nin/2), (Nin/2 + 1) -> (3Nin/4), and (3Nin/4 + 1) -> Nin (respectively), where Nin is the number of channels in the input RMF file. The compression factors are calculated assuming F1 = Ni/2 * 4/Nout and F2 = F1/2, F3 = F1/4, where Nout is the requested number of channels in the output RMF matrix. Nout must therefore be Nin/2 or smaller (by a factor divisible by 2) for FTRBNRMF to work in this mode. The net result is that the resultant RMF file has a linear channel-numbering scheme (equivalent to that used by the 'FAINT' datamode).

cmpmode='faint2bright'
This is a non-linear compression mode which should only be used on an ASCA SIS RMF which has the linear channel-numbering scheme appropriate for 'FAINT' datamode data, but which the user wishes to use in conjunction with an SIS PHA file constructed whilst the instrument was operating in 'BRIGHT' datamode. The mode is designed to essentially perform the opposite task to the 'BRIGHT2LINEAR' (see above). Again FTRBNRMF calculates and applies three separate compression factors (B1, B2 & B3) to the input RMF matrix over the input channel ranges 1 -> (Nin/4), (Nin/4 + 1) -> (Nin/2), and (Nin/2 + 1) -> Nin (respectively), where Nin is the number of channels in the input matrix. The compression factors are calculated assuming B1 = Ni/4 * 2/Nout and B2 = 2*B1, B3 = 4*B3, where Nout is the requested number of channels in the output RMF. Nout must be Nin/2 or smaller (by a factor divisible by 2) for FTRBNRMF to work in this mode. The net result is that the resultant RMF file has a NON-LINEAR channel-numbering scheme, equivalent to that used by the 'BRIGHT' datamode.

ENERGY COMPRESSION

The following modes of compression (only) are currently allowed when binning in energy-space :

cmpmode='ebinfile'
Read the binning information from the filename specified by the ebinfile parameter. This can be used to perform different linear compressions over different energy ranges.

cmpmode='optimal'
Use the energy optimal binning from Kaastra and Bleeker 2016, A&A 587, A151.

cmpmode='linear'
Perform linear binning using the factor given by the ebfact parameter.

WARNINGS ON USAGE

In order to minimise the disk-space requirements, the RMF matrix is stored in compressed form (CAL/GEN/92-002), that is all matrix elements below a given threshold (specified by LO_THRES keyword) are not stored. Unfortunately the LO_THRES keyword is not always used correctly, that is elements below this value are stored. When FTRBNRMF is used on such a matrix, the values below LO_THRES will NOT be stored. In order to overcome this, users may use the ftool/futil FPARKEY to change the LO_THRES keyword value in the input RMF file.

The non-linear compression modes available for use with ASCA SIS data should be used with extreme care. These FTRBNRMF modes are only required if users wish to perform spectral analysis on a PHA dataset taken in one on-board datamode in conjuncture with a detector response designed for use with PHA data obtained in the other datamode. Users are warned that it is not always immediately obvious if a PHA file using one channel-numbering scheme is used with a matrix using the other (though sharp discontinuities are a dead giveaway). Unfortunately, at the present time it is not possible to provide software checks for such errors, and it is the responsiblity of the user to determine & pay attention to the channel-numbering scheme used to construct the PHA & RMF files.

PARAMETERS

infile [filename]
The name of the FITS RMF file to be compressed

(ebdfile) [string]
The name of the input file with the EBOUNDS information. The Default, "%", means that it is same as infile.

(binfile='NONE') [filename]
The name of an ascii file specifying the channel binning information. NOTE the default for this is NONE. If a filename is specified then the parameters nchan and cmpmode are not prompted for. The ascii file format should be of the form :
1 256 2
where 1 is the starting channel, 256 the ending channel, and 2 the compression factor. NOTE : a compression factor of -1, omits the channel(s),ie:
1 250 2
251 256 -1
in this case channels 1 to 250 are rebinned by a factor of 2, and channels 251 to 256 are omitted. The number of channels in each entry should be the multiple of the compression factor.

(phafile='NONE') [filename]
The name of standard type I pha file from which to take a grouping (and quality) column to define the binning. If both the binfile and phafile parameters are set then the binfile will take precedence.

cmpmode [string]
The channel compression mode to be used. Currently the only values allowed are 'LINEAR', 'FAINT2BRIGHT' and 'BRIGHT2LINEAR' (see above), with 'LINEAR' as the default.

nchan [integer]
The number of channels required in the compressed RMF dataset when using one of the cmpmode options.

(ebinfile='NONE') [filename]
The name of an ascii file specifying the energy binning information. NOTE the default for this is NONE. If a filename is specified then the parameter ebfact is not prompted for. The ascii file format is identical to that given in the description of the binfile parameter.

(ebfact) [integer]
The compression factor for energy binning. This must be a divisor of the number of response energies in the input RMF.

outfile [filename]
The name of the FITS file to be written containing the compressed RMF dataset

(clobber = false) [boolean]
Flag specifying whether or not a pre-existing file with the same name as that requested as the output file from this task will be overwritten.

LAST MODIFIED

March 2018