OGIP Calibration Memo CAL/GEN/92-024
THE OGIP FORMAT FOR FILES
CONTAINING FILTER & WINDOW TRANSMISSIONS
(TRANSVER = 1992a)
Ian M George & Ron S Zellar
Mail Code 668,
NASA/GSFC,
Greenbelt,
MD20771.
Version: 1994 Aug 09
SUMMARY
| |
Ths document describes the standard format adopted by the OGIP for the
storage of the transmission of a filter or window in front of an instrument
as a function of energy, and position.
Intended audience: primarily OGIP programmers & hardware teams.
|
| |
Log of Significant Changes
| Release | Sections Changed | Brief Notes |
| Date | | |
| | |
| 1992 Jul 24 | First Draft
| (within memo CAL/GEN/92-003) |
| 1993 Oct 03 | All
| Separation from CAL/GEN/92-003 |
| 1994 Apr 29 | All | Reviewed & Updates |
| 1994 Aug 09 | All | General review/updates |
| | |
RELATED DOCUMENTATION
The following documents may also be of use:
- BCF & CPF Calibration File Guidelines
CAL/GEN/92-003 (George & Zellar)
- Calibration Index Files
CAL/GEN/92-008 (George, Pence & Zellar)
- Mandatory FITS Keywords for Calibration Files
CAL/GEN/92-011 (George, Zellar & Pence)
- Virtual Calibration Files
CAL/GEN/92-013 (George, Zellar & White)
- The OGIP Format for Vignetting Functions
CAL/GEN/92-021 (George & Zellar)
- The OGIP Format for Obscuration Factors
CAL/GEN/92-022 (George & Zellar)
1 Introduction
In the general case the transmission of a filter or window
consists of 3-dimensional
grid, Ttot, with axes photon energy (E), and two coordinates specifying
position of photon incidence (e.g. in physical
cartesian coordinates XPhy & YPhy across the window/filter).
Thus within the OGIP caldb both filter and window transmission
datasets are stored (in separate files) using an identical format
(with the CCNMxxxx codename used to distinguish between them),
comprising of two extensions:
- an extension containing the 3-d grid giving the transmission
at each E,XPhy,YPhy grid point
- an (optional) extension containing the corresponding atomic
data used construct the above transmissions (i.e. mass absorption
coefficients or cross-sections
as a function of E, and filter thickness as
a function of XPhy,YPhy).
Clearly the former is of most immediate use to s/w and users.
The latter was designed to provide users with the ability
to experiment with the nominal
filter/window thicknesses, composition or mass absortion coefficients.
Notes:
- The OGIP caldb distinguishes between filters and windows
purely on the basis of whether the structure is moveable:
filters being able to be physically removed from the
out of the optical path; windows being static fixtures
along in the line of sight.
- Multiple windows (or filters), consisting of
several layers of absorbing material, should be considered
as a single (compound) window from the calibration point of view.
Thus only a single calibration dataset is necessary.
This is true even if the windows/filters are physically separated
along the optical path (although not true if they are associated with
different physical components such if one is associated with
the detector, one with the X-ray mirror assembly).
- Many thin filters and windows require support structures in order to
maintain their rigidity.
In cases where this support is provided by the use of an underlying,
spatially-(psuedo)-uniform substrate, the opacity of the substrate as a
function of energy should be included in the transmission of the filter
as a whole as given in Section 2
(and the appropriate
atomic data included in the optional extension,
e.g. Section 2.2).
However in cases where (often additional) support is provided by a
spatially non-uniform structure (e.g. a wire mesh), the position and
transmission of this support structure is often stored separately
elsewhere.
The exact division of the calibration information between the two files
is highly instrument dependent.
1.1 Storage Options
For instruments containing both a filter and a window, separate BCFs
containing the respective transmission etc. should be created.
The extension containing the atomic data is not mandatory.
1.2 Dataset Origins & Storage Recommendations
The construction, format used (within the limitations discussed here)
and delivery of the data to the HEASARC (including any updates)
is the responsibility of the h/w teams and/or GOF.
However, below, are the recommendations of the HEASARC calibration team
based on their experience.
General
To avoid the chance of ambiguities,
it is strongly urged that both the above extensions are supplied to
the HEASARC.
No other specific issues.
Pre-launch
Prior to launch, the thickness of the flight filters are usually
measured at a limited number of positions during ground calibration
experiments and/or assumed from the h/w specifications.
The transmission functions are usually measured at a (limited)
number of photon energies during such experiemts
and/or calculated from atomic constants.
Post-launch
The transmission of a filter or window usually cannot be measured directly
in-orbit.
Rather, observations of standard cosmic sources (e.g. the Crab) combined
with spectral modelling enables the Spectral Response of the instrument
to be determined.
In the case of moveable filters, clearly a pair of such observations
- one with the filter in place, one with the filter removed - enables
the transmission to be calculated.
In the case of static filters/windows, the transmission cannot be
decoupled from the other components of the Spectral Response.
However, should should measurements reveal a discrepancy with
the expected spectral response which is identified with (or interpreted as)
a mis-calibration of the filter/window transmission(s),
h/w teams are urged to isolate and supply an updated dataset
to the HEASARC.
1.3 Dataset vs Task Summary
Due to the complexity of the Transmission of a filter or window as a
function of energy (as the result of sharp discontinuities due to atomic
processes etc. ), such a calibration dataset is not easily parameterized.
Thus, whilst theoretically possible, it is recommended that
Filter & Window Transmission datasets are not described by
a virtual calibration files (CAL/GEN/92-013).
It is strongly recommended that
the extension containing the atomic data should not be a virtual
either.
1.4 Software Considerations
Data Files:
Interpolation between the XPhy, YPhy
grid points is usually required.
By default, downstream software will use a simple 2-dimensional
linear interpolation when calculating the Transmission
between XPhy, YPhy grid points.
Thus the XPhy,YPhy grid should be of sufficient resolution
to enable this to be reasonable approximation.
As discussed in CAL/GEN/92-003 (George & Zellar),
it is strongly recommended
that the energy grid is of sufficient resolution and carefully chosen
such that interpolation of this parameter is not required.
However, in cases where interpolation is required, as simple
1-dimensional linear interpolation will be performed
(which will clearly be inaccurate close to sharp features).
Virtual Files:
Not applicable (see Section 1.3).
1.5 Relationships to Other Calibration Datasets
Downstream s/w should assume further calibration input is required
for a Window/Filter Transmission dataset under the following conditions:
and for the corresponding Atomic data extension under the following conditions:
A Window/Filter Transmission dataset is used in the construction
of the following calibration datasets:
- A CCNMxxxx = SPECRESP dataset, containing the total spectral
response of an instrument
The corresponding atomic data extensions is used in the construction
of the following calibration datasets:
- None (besides the transmission dataset discribed here)
2 Data File Formats
The dataset file formats currently allowed are:
- TRANSVER = 1992a, consisting of the mandatory extension
containing the transmissions (Section 2.1)
- FATVERSN = 1992a consisting of the optional extension
giving the effective window/filter surface densities (in units of
cm2 g−1), and mass absorption coefficients
from which the transmissions were calculated
(Section 2.2)
- FATVERSN = 1992b consisting of the optional extension
giving the effective window/filter thicknesses (in units of
cm), and absorption cross-sections
from which the transmissions were calculated
(Section 2.3)
However, see the comments in Section 1
regarding
the necessity of the optional extensions.
2.1 The Filter/Window Transmission Extension (TRANSVER = 1992a)
Description:
A single row BINTABLE extension for each window or filter on each
instrument containing
5 columns.
Extension Header
Beyond the standard FITS keywords required, the
following keywords/values are mandatory:
- TDIMnnn - the number of elements and ordering of the arrays
(see CAL/GEN/92-003; George & Zellar 1992)
of each multi-dimensional array.
Only the TRANSMIS column here (with nnn=5 in the example below).
- CSYSNAME - the spatial coordinate system in use
(see CAL/GEN/92-003; George & Zellar 1992)
(CSYSNAME = PHY_DET is assumed in the example
below)
and the following keywords/values are mandatory for CIF purposes
(see CAL/GEN/92-011; George, Zellar & Pence 1992):
- TELESCOP - the name of the staellite/mission.
Allowed values are given in CAL/GEN/92-011.
- INSTRUME - the name of the telescope mirror/collimator
assembly or detector.
Allowed values are given in CAL/GEN/92-011.
It should be noted that this keyword is used to further clarify the
physical location of the filter/window concerned. For example a protective
window on the front of the X-ray mirror assembly/collimator of an
instrument would have INSTRUME = XMA (where XMA is an allowed
value listed in CAL/GEN/92-011), whilst the front (or internal)
window on a detector DET would have INSTRUME = DET (where again
DET is an allowed value as listed in CAL/GEN/92-011).
- FILTER - (for CCNM0001 = FTRANS datasets only) the name of
filter.
Allowed values are given in CAL/GEN/92-011.
- CCLS0001 (=BCF) - the OGIP class of this calibration file
- CDTP0001 (=DATA) - the OGIP class of the data type
- CCNM0001 - the OGIP codename for the contents
- CCNM0001 = FTRANS, for a filter transmission
- CCNM0001 = WTRANS, for a window transmission
- CBDn0001 - the parameter limitation of the dataset (see below)
- CVSD0001 - calibration validity start date
- CVST0001 - calibration validity start time
- CDES0001 - a descriptive string of the calibration dataset
and the following mandatory to supply further information:
- TRANSVER - the OGIP version of the FITS format in use
(in this case 1992a)
Data Format:
The data within this extension is organised as a BINTABLE with the
following columns:
- Elow, a fixed-length REAL vector (array, each element within
which is 4-byte) containing the lower energy bounds of
the energy bins.
The FITS column name is ENERG_LO.
The recommended units are keV.
- Ehigh, a fixed-length REAL vector (array, each element within
which is 4-byte) containing the upper energy bounds of
the energy bins.
The FITS column name is ENERG_HI.
The recommended units are keV.
- XPhy, a fixed-length REAL vector (array, each element within
which is 4-byte) containing the physical X-coordinates.
The FITS column name is PHYX (but see below).
The recommended units are mm.
- YPhy, a fixed-length REAL vector (array, each element within
which is 4-byte) containing the physical Y-coordinates.
The FITS column name is PHYY (but see below).
The recommended units are mm.
- Ttot, a fixed length REAL vector (array, each element within
which is 4-byte) containing the transmission of the filter/window
at each
E,XPhy,YPhy grid point.
The FITS column name is TRANSMIS.
The order of data storage is
Ttot (E,XPhy,YPhy),
where E represents the
Elow and Ehigh array (see below).
(unitless).
These are summarized in Table 1.
Table 1: Summary of the OGIP format for
Filter/Window Transmissions (TRANSVER = 1992a).
to (filename).(ext)
Name: TRANSMISSION
Version: TRANSVER = 1992a
Description: Transmission as a function of energy and position
for filters and windows
An alternate spatial coordinate frame may also be used (see text).
Optional columns containing the statistical and systematic error arrays
are not shown.
Format: BINTABLE
| column |
| 1 | 2 | 3 | 4 | 5 |
| | | | |
| contents |
| Low energy | High energy | Position Grid coords | Transmission |
| bounds | bounds | | | |
| | | | |
| Elow | Ehigh | XPhy | YPhy | Ttot |
| |
| format of each column |
| 4-byte | 4-byte | 4-byte | 4-byte | 4-byte |
| real | real | real | real | real |
| array | array | array | array | array |
| |
| total number of elements per row |
| i | i | j | j | i ×j |
| |
| column name |
| ENERG_LO | ENERG_HI | PHYX | PHYY | TRANSMIS |
| | | | |
Points to Note & Conventions
- The ordering of the columns is of course arbitrary, however that
used here is recommended.
- The rules and conventions concerning the energy grid
(Elow & Ehigh)
given in CAL/GEN/92-003 apply.
- An alternate spatial coordinate frame may be used, in which case
- the values of the CSYSNAME keyword should be replaced
by the appropriate string listed in
CAL/GEN/92-003
- and/or (if necessary) the PHYX & PHYY column names replaced
by more suitable alternatives if a different coordinate
notation is employed. In this case the CSYSNAME keyword
is mandatory and should give the column names used
(see CAL/GEN/92-003).
- The parameter-space limitations on the dataset involving the
following pname strings are recommended to be specified
via the CBDn0001 keywords (see CA:/GEN/92-003):
- pname = PHYX & PHYY - giving the range of detector
positions for
which the dataset is valid;
(or corresponding alternate values of pname if a different coordinate
notation is employed)
along with any other limitations the authors consider necessary.
- Alternative physical units are allowed for all columns of the table
as long as they conform to the rules given in CAL/GEN/93-001.
The same is true for the physical units associated with the
CBDn0001 keywords.
- Datasets in which T_tot is independent of either
spatial coordinate
should NOT contain the corresponding column.
It is recommended that a COMMENT card is used within the header to
explain this fact to human readers (eg see Section 5.1).
- The order of Ttot (E,XPhy, YPhy)
whereby energy parameters
changes fastest, and (arbitarily) the YPhy parameter slowest
was
chosen to facilitate access for the most common applications:
interpolation in XPhy,YPhy-space of Ttot vs
Elow,Ehigh arrays.
This ordering is further confirmed
by the value of the mandatory TDIMnnn and iCTYPnnn keywords
(where nnn is the column number, and i the axis number).
The rules and conventions governing these keywords
are given in CAL/GEN/92-003
(see also Section 5).
- The optional arrays containing the 1σ statistical error
associated
with each element of Ttot
(if required)
should be contained in additional columns named
STAT_MIN (for the negative error) and
STAT_MAX (for the positive error).
Similarly, the optional arrays containing
the 1σ fractional systematic error
associated
with each element of Ttot
(if required)
should be contained in additional columns named
SYS_MIN (for the negative error) and
SYS_MAX (for the positive error).
The rules and conventions governing such arrays (if present)
are given in CAL/GEN/92-003.
These arrays are provided here for completeness, and rarely
either provided by the h/w teams or used by downstream s/w.
2.2 Filter Atomic Data Extension (FATVERSN = 1992a)
This (optional) extension was
originally designed to provide users with the ability
(should they wish) to experiment with the nominal
filter/window thicknesses, composition or mass absortion coefficients.
However, following the design of formats for
General Atomic (Section ) and Filter/Window Thickness
(Section ) datasets, the necessity for this extension
has reduced.
Therefore, if General Atomic and Filter/Window Thickness datasets
are supplied for a given instrument, this extension
is not required.
Description:
There are two types of calibration information stored within this
single (optional) extension:
- the mass absorption coefficient (Kabsj, in units of
cm2 g−1) as a function of
energy (E) for each of the j
components of the filter/window
- the effective surface
thickness (Lthickj, in units of g cm−2)
of each of these components as
a function of position (XPhy,YPhy etc. ) on the filter/window.
Thus the transmission Tj at an energy E and position XPhy,YPhy
of the jth component within the
filter/window is given by
|
Tj (E) = exp(− Lthickj ×Kabsj(E) ) |
| (1) |
where Lthickj ( = ρ×d) is the surface density of
atom/molecule j
(Lthickj = ρ×d where mj is the mass
of an atom/molecule of j and ρ the denisty).
The total transmission Ttot of the complete filter/window
(including all ncomp components) at a given E,XPhy,YPhy
(i.e. as stored explicitly in the Transmission extension,
e.g. see Section 2.1) is given by
|
Ttot (E,XLin,YLin) = |
ncomp
∏
j=1
|
Tj (E,XLin,YLin) |
| (2) |
Extension Header
Beyond the standard FITS keywords required, the
following keywords/values are mandatory:
- TDIMnnn - the number of elements and ordering of the arrays
(see CAL/GEN/92-003; George & Zellar 1992)
of each multi-dimensional array.
Only the MASS_ABS & THICKNES columns here
(with nnn=4 & 7 respectively in the example below).
- CSYSNAME - the spatial coordinate system in use
(see CAL/GEN/92-003; George & Zellar 1992)
(CSYSNAME = PHY_DET is assumed in the example
below)
and the following keywords/values are mandatory for CIF purposes
(see CAL/GEN/92-011; George, Zellar & Pence 1992):
- TELESCOP - the name of the staellite/mission.
Allowed values are given in CAL/GEN/92-011.
- INSTRUME - the name of the telescope mirror/collimator
assembly or detector.
Allowed values are given in CAL/GEN/92-011.
It should be noted that this keyword is used to further clarify the
physical location of the filter/window concerned.
See the corresponding discussion in Section 2.1.
- CCLS0001, 0002 (=BCF) - the OGIP class of this calibration file
- CDTP0001, 0002 (=DATA) - the OGIP class of the data type
- CCNM0001 - the OGIP codename for the contents
- CCNM0001 = FATOM, for atomic data related to
a filter transmission ... under revision
- CCNM0001 = WATOM, for atomic data related to
a window transmission ... under revision
- CCNM0002 = FTHICK, for the thickness of a filter
- CCNM0002 = WTHICK, for the thickness of a window
- CBDn0001, 0002 - the parameter limitation of the dataset (see below)
- CVSD0001, 0002 - calibration validity start date
- CVST0001, 0002 - calibration validity start time
- CDES0001, 0002 - a descriptive string of the calibration dataset
and the following mandatory to supply further information:
- FATVERSN - the OGIP version of the FITS format in use
(in this case 1992a)
Data Format:
The data within this extension is organised as a BINTABLE with the
following columns:
- Elow, a fixed-length REAL vector (array, each element within
which is 4-byte) containing the lower energy bounds of
the energy bins.
The FITS column name is ENERG_LO.
The recommended units are keV.
- Ehigh, a fixed-length REAL vector (array, each element within
which is 4-byte) containing the upper energy bounds of
the energy bins.
The FITS column name is ENERG_HI.
The recommended units are keV.
- Comp, a fixed-length CHARACTER vector (array, each element within
which is 10-bytes) containing the names/symbols of
each component of the filter/window.
The FITS column name is COMPNAME.
(unitless)
- Kabsj, a fixed-length REAL vector (array, each element within
which is 4-byte) containing the mass absorption coefficient for
each component j of the filter/window.
The FITS column name is MASS_ABS.
The recommended units are cm2 g−1.
- XPhy, a fixed-length REAL vector (array, each element within
which is 4-byte) containing the physical X-coordinates.
The FITS column name is PHYX (but see below).
The recommended units are mm.
- YPhy, a fixed-length REAL vector (array, each element within
which is 4-byte) containing the physical Y-coordinates.
The FITS column name is PHYY (but see below).
The recommended units are mm.
- Lthick, a fixed length REAL vector (array, each element within
which is 4-byte) containing the effective
surface density thickness at each
E,XPhy,YPhy grid point for each
component j of the filter/window.
The FITS column name is THICKNES.
The order of data storage is
Lthick (E,XPhy,YPhy,Comp),
where E represents the
Elow and Ehigh array (see below).
The recommended units are g / cm−2.
These are summarized in Table 2.
Table 2: Summary of the OGIP format for
Filter/Window Atomic Data (FATVERSN = 1992a).
to (filename).(ext)
Name: FATOM or WATOM
Version: FATVERSN = 1992a
Description: Atomic Data required to calculate the
transmission of a filter/window as a function of energy and position.
An alternate spatial coordinate frame may also be used (see text).
Optional columns containing the statistical and systematic error arrays
are not shown.
Format: BINTABLE
| column |
| 1 | 2 | 3 | 4 | 5 | 6 | 7 |
| | | | | | |
| contents |
| Low energy | High energy | Component | Mass Absorption | Position Grid coords | Surface |
| bounds | bounds | Name | Coefficient | | | Density |
| | | | | | |
| Elow | Ehigh | Comp | Kma | XPhy | YPhy | Lthick |
| |
| format of each column |
| 4-byte | 4-byte | 10-byte | 4-byte | 4-byte | 4-byte | 4-byte |
| real | real | character | real | real | real | real |
| array | array | array | array | array | array | array |
| |
| total number of elements per row |
| i | i | j | i ×j | k | k | k ×j |
| |
| column name |
| ENERG_LO | ENERG_HI | COMPNAME | MASS_ABS | PHYX | PHYY | THICKNES |
| | | | | | |
Points to Note & Conventions
- The ordering of the columns is of course arbitrary, however that
used here is recommended.
- The rules and conventions concerning Elow & Ehigh
given in CAL/GEN/92-003 apply.
- An alternate spatial coordinate frame may be used, in which case
- the values of the CSYSNAME keywords should be replaced
by the appropriate string listed in
CAL/GEN/92-003
- and/or (if necessary) the PHYX & PHYY column names replaced
by more suitable alternatives if a different coordinate
notation is employed. In this case the CSYSNAME keyword
is mandatory and should give the column names used
(see CAL/GEN/92-003)
Physical or Detector coordinates are strongly recommended.
- Datasets in which Lthick is independent of either
spatial coordinate
should NOT contain the corresponding column.
It is recommended that a COMMENT card is used within the header to
explain this fact to human readers.
- The order of Lthick (E,XPhy, YPhy, Comp)
whereby energy parameters
changes fastest, and the Comp parameter slowest
was
chosen to facilitate access for the most common applications:
interpolation in XPhy,YPhy-space of Ttot vs
Elow,Ehigh arrays for individual components.
This ordering is further confirmed
by the value of the mandatory TDIMnnn and iCTYPnnn keywords
(where nnn is the column number, and i the axis number).
The rules and conventions governing these keywords
are given in CAL/GEN/92-003.
- The optional arrays containing the 1σ statistical error
associated
with each element of Kma
(if required)
should be contained in additional columns named
MAST_MIN (for the negative error) and
MAST_MAX (for the positive error).
Similarly, the optional arrays containing
the 1σ fractional systematic error
associated
with each element of Lthick
(if required)
should be contained in additional columns named
MASY_MIN (for the negative error) and
MASY_MAX (for the positive error).
- The optional arrays containing the 1σ statistical error
associated
with each element of Lthick
(if required)
should be contained in additional columns named
STAT_MIN (for the negative error) and
STAT_MAX (for the positive error).
Similarly, the optional arrays containing
the 1σ fractional systematic error
associated
with each element of Lthick
(if required)
should be contained in additional columns named
SYS_MIN (for the negative error) and
SYS_MAX (for the positive error).
The rules and conventions governing such arrays (if present)
are given in CA:/GEN/92-003.
These arrays are provided here for completeness, and rarely
either provided by the h/w teams or used by downstream s/w.
2.3 Filter Atomic Data Extension (FATVERSN = 1992b)
As for comments in Section 2.2.
Description:
There are four types of calibration information stored within this
single (optional) extension:
- the total absorption cross-section (σabsj, in units of
cm2) as a function of
energy (E) for each of the j
components of the filter/window
- the mass (mj, in units of
g) of a single atom/molecule of each of the j
components of the filter/window
- the density (ρj, in units of
g / cm−3) of each of the j
components of the filter/window
- the effective thickness
(dj, in units of cm)
of each of these components as
a function of position (XPhy,YPhy etc. ) on the filter/window.
Thus the transmission Tj at an energy E and position XPhy,YPhy
of the jth component within the
filter/window is given by
|
Tj (E) = exp |
|
− |
ρ
mj
|
× σabsj(E) × dj |
|
|
| (3) |
The total transmission Ttot of the complete filter/window
(including all ncomp components) at a given E,XPhy,YPhy
(i.e. as stored explicitly in the Transmission extension,
e.g. see Section 2.1) is given by
Equation 2
(Section 2.2).
Extension Header
As in Section 2.2, except that:
- TDIMnnn - the number of elements and ordering of the arrays,
is required for the ABS_XSECT, MASS, DENSITY
& THICKNES columns below.
- Mandatory CIF keywords are required for all 4 calibration
datasets. These are straightforward, except:
- CCNM0001 = FATOM (or WATOM) ... under revision
- CCNM0002 = MASS ... under revision
- CCNM0003 = DENS ... under revision
- CCNM0004 = FTHICK (or WTHICK) ... under revision
- FATVERSN (= 1992b)
Data Format:
The data within this extension is organised as a BINTABLE with the
following columns:
- Elow, a fixed-length REAL vector (array, each element within
which is 4-byte) containing the lower energy bounds of
the energy bins.
The FITS column name is ENERG_LO.
The recommended units are keV.
- Ehigh, a fixed-length REAL vector (array, each element within
which is 4-byte) containing the upper energy bounds of
the energy bins.
The FITS column name is ENERG_HI.
The recommended units are keV.
- Comp, a fixed-length CHARACTER vector (array, each element within
which is 10-bytes) containing the names/symbols of
each component of the filter/window.
The FITS column name is COMPNAME.
(unitless)
- σabsj,
a fixed-length REAL vector (array, each element within
which is 4-byte) containing the absorption cross-section for
each component j of the filter/window.
The FITS column name is ABS_XSECT.
The recommended units are cm2.
- mj,
a fixed-length REAL vector (array, each element within
which is 4-byte) containing the mass of one atom/moelcule
of each component j of the filter/window.
The FITS column name is MASS.
The recommended units are g.
- ρj,
a fixed-length REAL vector (array, each element within
which is 4-byte) containing the density of
each component j of the filter/window.
The FITS column name is DENSITY.
The recommended units are g / cm−3.
- XPhy, a fixed-length REAL vector (array, each element within
which is 4-byte) containing the physical X-coordinates.
The FITS column name is PHYX (but see below).
The recommended units are mm.
- YPhy, a fixed-length REAL vector (array, each element within
which is 4-byte) containing the physical Y-coordinates.
The FITS column name is PHYY (but see below).
The recommended units are mm.
- d(j), a fixed length REAL vector (array, each element within
which is 4-byte) containing the effective
thickness at each
E,XPhy,YPhy grid point for each
component j of the filter/window.
The FITS column name is THICKNES.
The order of data storage is
dj (E,XPhy,YPhy,Comp),
where E represents the
Elow and Ehigh array (see below).
The recommended units are g / cm−2.
These are summarized in Table 3.
Table 3: Summary of the OGIP format for
Filter/Window Atomic Data (FATVERSN = 1992b).
to (filename).(ext)
Name: FATOM or WATOM
Version: FATVERSN = 1992b
Description: Atomic Data required to calculate the
transmission of a filter/window as a function of energy and position.
An alternate spatial coordinate frame may also be used (see text).
Optional columns containing the statistical and systematic error arrays
are not shown.
Format: BINTABLE
| column |
| 1 | 2 | 3 | 4 | 5 | 6 |
| | | | | |
| contents |
| Low energy | High energy | Component | Total Absorption | Mass per | Density |
| bounds | bounds | Name | Cross-Section | atom/moelcule | |
| | | | | |
| Elow | Ehigh | Comp | σabsj | mj | ρj |
| |
| format of each column |
| 4-byte | 4-byte | 10-byte | 4-byte | 4-byte | 4-byte |
| real | real | character | real | real | real |
| array | array | array | array | array | array |
| |
| total number of elements per row |
| i | i | j | i ×j | i ×j | i ×j |
| |
| column name |
| ENERG_LO | ENERG_HI | COMPNAME | ABS_XSECT | MASS | DENSITY |
| | | | | |
| column |
| 7 | 8 | 9 |
| | |
| contents |
| Position Grid coords | Component |
| | Thickness |
| | |
| XPhy | YPhy | dj |
| |
| format of each column |
| 4-byte | 4-byte | 4-byte |
| real | real | real |
| array | array | array |
| |
| total number of elements per row |
| k | k | k ×j |
| |
| column name |
| PHYX | PHYY | THICKNES |
| | |
Points to Note & Conventions
- The ordering of the columns is of course arbitrary, however that
used here is recommended.
- The rules and conventions concerning Elow & Ehigh
given in CAL/GEN/92-003 apply.
- An alternate spatial coordinate frame may be used, in which case
- the values of the CSYSNAME keywords should be replaced
by the appropriate string listed in
CAL/GEN/92-003
- and/or (if necessary) the PHYX & PHYY column names replaced
by more suitable alternatives if a different coordinate
notation is employed. In this case the CSYSNAME keyword
is mandatory and should give the column names used
(see CAL/GEN/92-003).
Physical or Detector coordinates are strongly recommended.
3 Virtual File Formats & Allowed Standalone Tasks
As noted in Section 1.3, given the difficulty
parameterizing the Filter transmission in energy-space, it is not recommended
that such datasets are stored as Virtual Calibration Files.
4 Related Software
The following list of subroutines/tasks are available:
- FORTRAN subroutine wttrs1.f (callib)
writes an TRANSVER = 1992a dataset
(Section 2.1)
5 Example FITS headers
Below are several examples of files currently available within the
OGIP Caldb. Note that the authors of datasets are encouraged to
supply copious COMMENT cards to aide human readers.
Follows is the header from an extension containing a TRANSVER=1992a dataset.
The Window Transmission dataset
is stored in column 3 and is a function of 729 energies.
There is no THETA or PHI dependence for this dataset.
The iCTYP3 and TDIM4 keywords confirm that there is only one
dimension to the array, and that that axis is 'ENERGY'.
XTENSION= 'BINTABLE' / binary table extension
BITPIX = 8 / 8-bit bytes
NAXIS = 2 / 2-dimensional binary table
NAXIS1 = 8748 / width of table in bytes
NAXIS2 = 1 / number of rows in table
PCOUNT = 0 / size of special data area
GCOUNT = 1 / one data group (required keyword)
TFIELDS = 3 / number of fields in each row
TTYPE1 = 'ENERG_LO' / Lower boundaries of energy bins
TFORM1 = '729E ' / data format of the field: 4-byte REAL
TUNIT1 = 'keV ' / physical unit of field
TTYPE2 = 'ENERG_HI' / Upper boundaries of energy bins
TFORM2 = '729E ' / data format of the field: 4-byte REAL
TUNIT2 = 'keV ' / physical unit of field
TTYPE3 = 'TRANSMIS' / Transmission dataset
TFORM3 = '729E ' / data format of the field: 4-byte REAL
EXTNAME = 'TRANSMISSION' / name of this binary table extension
HDUCLASS= 'OGIP ' / format conforms to OGIP standard
HDUCLAS1= 'RESPONSE' / dataset relates to instrument response
HDUVERS1= '1.0.0 ' / Version of family of formats
HDUCLAS2= 'TRANSMISSION' / dataset is a transmission
HDUVERS2= '1.1.0 ' / Version of format (OGIP memo CAL/GEN/92-024)
HDUCLAS3= 'WINDOW ' / for device given by INSTRUME (+DETNAM) kywrd
CSYSNAME= 'XMA_POL ' / spatial coord system used in this dataset
TELESCOP= 'ROSAT ' / mission/satellite name
INSTRUME= 'PSPCB ' / instrument/detector name
FILTER = 'NONE ' / filter in use
COMMENT Dataset assumed to be independent of THETA
COMMENT Dataset assumed to be independent of PHI
TDIM3 = '(729) ' / Ordering of n-d TRANSMIS array
1CTYP3 = 'ENERGY ' / Axis of 1st dimension of TRANSMIS array
TRANSVER= '1992a ' / OGIP classification of FITS format
HISTORY Extension written by WTTRS1 1.1.0
COMMENT
COMMENT The following keywords are required for the OGIP CALDB
CCLS0001= 'BCF ' / OGIP class of calibration file
CDTP0001= 'DATA ' / OGIP type of dataset (DATA, TASK etc)
CCNM0001= 'WTRANS ' / OGIP codename for this type of cal file
CVSD0001= '01/06/90' / Dataset validity start date (UTC)
CVST0001= '00:00:00' / Dataset validity start time (UTC, of day CVSD)
CDES0001= 'PSPCB Window Transmission (version 1); 729 energies'
CBD10001= 'THETA(0-60.0)arcmin' / dataset parameter boundary
CBD20001= 'PHI(0-360)deg' / dataset parameter boundary
CBD30001= 'ENERG(0.0546-3.01)keV' / dataset parameter boundary
COMMENT
COMMENT NOTES: 1994 Jul 21 (Ian M George, HEASARC)
COMMENT ------------------
COMMENT This dataset was converted to OGIP FITS format by
COMMENT Ian M George (HEASARC) from the ASCII file
COMMENT pspc_b_win.asc
COMMENT supplied by Steve Snowden (ROSAT GOF, NASA/GSFC).
COMMENT
REFERENCES
Angelini, L., et al.,
1992.
In preparation.
George, I.M.,
1992. Legacy, 1, 56,
(CAL/GEN/91-001).
George, I.M. & Zellar, R.S.,
1992. OGIP Calibration Memo CAL/GEN/92-003.
(available on-line from the anon ftp account on
legacy.gsfc.nasa.gov).
George, I.M., Zellar, R.S. & Pence, W.,
1992. OGIP Calibration Memo CAL/GEN/92-011.
(available on-line from the anon ftp account on
legacy.gsfc.nasa.gov).
George, I.M., Arnaud, K.A., Pence, W. & Ruamsuwan, L.,
1992a.
(CAL/GEN/92-002).
George, I.M., et al.,
1992b. In preparation.
(CAL/SW/92-004).
File translated from
TEX
by
TTH,
version 3.49.
On 8 Apr 2004, 11:04.