SPEX User's Manual - SRON

108 Response matrices
practical problems. For example, the fitsio-package allows a maximum of 1000 extensions. The documentation
of fitsio says that this number can be increased, but that the access time to later extensions
in the file may become very long.
In principle we want to allow for data sets with an unlimited number of response components. For
example, when a cluster spectrum is analysed in 4 quadrants and 10 radial annuli, one might want
to extract the spectrum in 40 detector regions and model the spectrum in 40 sky sectors, resulting in
principle in at least 1600 response components (this may be more if the response for each sky sector and
detector region has more components).
Therefore I propose to use only three additional and mandatory extensions.
The first extension is a binary table with 4 columns and contains for each component the number of data
channels, model energy bins, sky sector number and detector region number (see table 5.8).
The second extension is a binary table with 5 columns and contains for each model energy bin for each
component the lower model energy bin boundary (keV), the upper model energy bin boundary (keV),
the starting data channel, end data channel and total number of data channels for the response group
(see table 5.9).
The third extension is a binary table with 2 columns and contains for each data channel, for each model
energy bin for each component the value of the response at the bin center and its derivative with respect
to energy (see table 5.10). SI units are mandatory (i.e. m 2 for the response, m 2 keV −1 for the response
derivative).
Table 5.8: First extension to the response file
keyword
EXTNAME (=RESP INDEX)
NAXIS1 = 16
NAXIS2 =
NSECTOR =
NREGION =
NCOMP =
TFIELDS = 4
TTYPE1 = ’NCHAN’
TTYPE2 = ’NEG’
TTYPE3 = ’SECTOR’
TTYPE4 = ’REGION’
description
Contains the basic indices for the components in the form
of a binary table
There are 16 bytes in one row
This number corresponds to the total number of components
(the number of rows in the table)
This 4-byte integer is the number of sky sectors used.
This 4-byte integer is the number of detector regions used.
This 4-byte integer is the totalnumber of response components
used (should be equal to NAXIS2).
The table has 4 columns; all columns are written as 4-byte
integers (TFORM=’1J’)
First column contains the number of data channels for each
component. Not necessarily the same for all components,
but it must agree with the number of data channels as
present in the corresponding spectrum file.
Second column contains the number of model energy grid
bins for each component. Not necessarily the same for all
components.
Third column contains the sky sector number as defined by
the user for this component. In case of simple spectra, this
number should be 1.
Fourth column contains the detector region number as defined
by the user for this component. In case of simple spectra,
this number should be 1.