RBNRMF (Oct06) ftools.caltools RBNRMF (Oct06) NAME rbnrmf -- Physically compresses (rebins) an RMF dataset in channel-space and/or energy space. USAGE rbnrmf infile [ebdfile] [binfile] [fchan] nchan cmpmode [ebinfile] [ebfact] outfile [chatter] [clobber] DESCRIPTION RBNRMF 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 RBNRMF 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 mode (or 'type') of compression performed is specified via the user-defined "cmpmode" parameter. The hidden parameter fchan allows the users to define the first channel no. in the output file. There are three options as follows: (1) fchan=% (by default) which means that the first channel no. in output is same as the first channel no. in input. (2) fchan=0 which means that whatever be the first channel no. in input file, the output first channel no. is zero. (3) fchan=1 which means that whatever be the first channel no. in input file, the output first channel no. is one. CHANNEL COMPRESSION MODES The following modes of compression (only) are currently allowed when binning in channel-space : cmpmode='LINEAR' In most cases (ie for most instruments & operating modes) only a LINEAR compression is allowed. In such cases the compression is such that 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, RBNRMF 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 RBNRMF 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 RBNRMF 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 RBNRMF 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 Only linear binning is allowed when compressing in energy-space. If the ebinfile parameter is set then this file is used to get the compression information otherwise a linear compression with binning factor ebfact is performed. 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 RBNRMF 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 RBNRMF 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 [character string] The name of the FITS RMF file to be compressed (ebdfile) [character string] The name of the FITS EBD input file. The Default, "%", means that it is same as infile. (binfile='NONE') [character string] 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. (fchan=%) [character string] The option to define the output first channel no. By default(%) it is same as input. nchan [integer] The number of channels required in the compressed RMF dataset cmpmode [character 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. (ebinfile='NONE') [character string] 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 [character string] The name of the FITS file to be written containing the compressed RMF dataset (chatter = 9) [integer] Flag to indicate how chatty the task is at execution. A value of 9 is the default, with lower/higher values producing quieter/verbose output respectively. (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. EXAMPLES 1. To compress the channel-space in "my_file.rmf" to obtain a new file with 512 channels, with linear compression mode : ca> rbnrmf my_file.rmf 512 linear compress.rmf 2. Suppose my_file has 1024 channels and 2048 energy bins and we wish to bin up in energy space to give 1024 bins : ca> rbnrmf my_file.rmf 1024 linear compress.rmf ebfact=2 BUGS None known SEE ALSO CAL/GEN/92-002 (George etal 1992 Legacy, 2, 51), CAL/GEN/92-002a the ftools/heasarc task rbnpha LOG OF SIGNIFICANT CHANGES v5.0.0 (2006 Oct) Added binning in energy space. v4.4.0 (1998 Jun) Modify the rebinning algorithm. Preserve the group structure. v4.2.0 (1996 Nov) Added option of specifying first output channel no. v3.0.0 (1995 Aug) Added option of specifying binning in an ascii file v2.0.0 (1994 Mar) Added dynamic memory allocation v1.0.0 (1993 Oct) Initial public release PRIMARY AUTHOR Rehana Yusaf HEASARC NASA/GFSC http://heasarc.gsfc.nasa.gov/cgi-bin/ftoolshelp (301) 286-6115